MASKANA.Vol. 9, Ed. 2,
41-51, 2018
https://doi.org/10.18537/=
mskn.09.02.06
Š Author(s) 2018. This work is
distributed under the Creative Commons Attribution 4.0 License.
Review
Article
A province with several climates: What knowledge of hydrology can be
useful? A literature review
Department of Hydraulic Engineering,
Pontificia Universidad Católica del Ecuador, 130103 Portoviejo, Ecuador.
Autor para correspondencia: andygiler90@hotmail.es
Fecha de recepción: 13 de agosto 2018 - Fecha de aceptación: 28 de agos=
to
2018
This article explores the hydrological state of the
art that could be useful for a climate-diverse region, such as Manabí provi=
nce
in Ecuador. The province, with an area of 18,940 km2, has a vari=
ety
of tropical and dry climates. First, a review of the climatic conditions of=
the
study area is carried out, since different sources disagree to some extent
regarding climate types; then, a critical assessment of the relevant hydrol=
ogic
literature is carried out. Here it is found that the literature best-suited=
for
the conditions of Manabí includes literature for semi-arid, savannah and hu=
mid
tropical hydrology. Several research gaps are found, but also a significant
body of knowledge that could serve as a base for future studies. It should =
be
noted that much of the available literature was obtained with vegetation and
soil conditions that might differ from those of Manabí. Therefore, it is
essential that findings from abroad are contrasted with results obtained in
Manabí. Understanding of the hydrological functioning of the study area cou=
ld
contribute to the hydrologic literature for semi-arid, savannah and humid
tropic climates.
Keywords:=
Hydrology, semi-arid, savannah, humid tropics, Köppen-Geiger
climate classification, Ecuador coast, Manabí.
RESUMEN
El
presente artículo explora el estado de la ciencia hidrológica que podría ser
útil para una región con diversidad climática tal como lo es la provincia de
Manabí en Ecuador. La provincia de Manabí, con un área de 18,940 km2,
tiene una variedad de climas tropicales y secos. Primero, se lleva a cabo u=
na
revisión de las condiciones climáticas del área de estudio, ya que diferent=
es
fuentes discrepan, en cierta medida, con respecto a los tipos de clima; lue=
go,
se lleva a cabo una evaluación crítica de la literatura hidrológica relevan=
te.
Aquí se encuentra que la literatura más adecuada para las condiciones de Ma=
nabí
incluye literatura para hidrología semiárida, sabana y tropical húmeda. Aun
cuando se encontró vacíos de investigación, también existe una cantidad
significativa de conocimiento, utilizable como base en futuros estudios. Ca=
be
seńalar que gran parte de la literatura disponible se obtuvo con condicione=
s de
vegetación y suelo que podrían diferir de las de Manabí. Por lo tanto, es
esencial que resultados de otros sitios de estudio se contrasten con aquell=
os
obtenidos en Manabí. El entendimiento del funcionamiento hidrológico en el =
área
de estudio podría contribuir a la literatura de hidrología para climas
semiárido, de sabana y tropical húmedo.
=
Manabí is a province of 18,940 km2 loca=
ted
in Ecuadors coastal region. According to the recently updated Köppen-Geiger classifications has Manabí at least thr=
ee
climates: semi-arid (BSh), savannah (Aw and
Since Petheram et al. (2012) claim that most of t=
he
worlds population growth to 2050 is projected to occur in the tropics, the=
re
is a serious need for robust methods for water resource assessments to unde=
rpin
the sustainable management of water in these regions. Authorities need clea=
r,
visible and reliable information to be able to make well-informed decisions=
. In
terms of water resources, having a variety of climates gives policy makers =
and
practitioners more options, but at the same time, it can make management mo=
re
challenging. Authorities ought more than ever before to make decisions base=
d on
scientific evidence. Unfortunately, at present, much of the evidence needed=
is
not available, or has little visibility in Manabí and for regions with simi=
lar
climates (Hughes, Heal, & Leduc, 2017)=
.
In general, not a great deal of scientific literat=
ure
has been generated in Manabí, nor in Ecuador as a whole (Feyen, Mila, Van Hoof, Quinde, Ochoa, & Bojorque, 2016; Semperteg=
ui,
Torres, Gallardo, & Hernández, 1990). This also applies to the
fields of hydrology, meteorology and ecology. Often, methods and models from
temperate regions are employed without considering that these models could =
have
been developed under different climatic conditions. The findings thus may n=
ot
be applicable to Manabí and regions with similar climates. Furthermore,
different sources of climatic information disagree to some extent with the
climates in Manabí, making comparison with literature from other regions mo=
re
challenging and less accurate. This creates confusion for researchers and
practitioners.
The aim of this research is to review the hydrolog=
ical
state of the art that could be useful for a climate-diverse region like Man=
abí
province in Ecuador. To achieve that, a review of the climatic conditions of
the study area (Section 1) is first carried out; then, a critical assessmen=
t of
the relevant hydrologic literature is conducted, highlighting gaps in resea=
rch
(Section 2).
The literature review is based on local and
international relevant scientific literature, government and Non-Government=
al
Organization (NGO) reports and press articles. Geographical Information Sys=
tems
(GIS) were used to generate basic maps and figures, and when pictures were
taken from other studies the source was acknowledged.
Manabí province is a province with an area of about
19,000 km2, located in Ecuadors coastal region, is traversed by=
the
equatorial line (0°00), and the El Nińo (ENSO) and Humboldt currents are
usually present. The elevation ranges from sea level on the Pacific Ocean c=
oast
to about 500 meters above sea level (m.a.s.l) i=
n the
easternmost part. The province is often subject to droughts and flooding. In
order to overcome these issues, structural measures including dams, irrigat=
ion
systems, and major flood protection schemes were put in place, starting in =
1971
with the Poza Honda dam (OAS, Republica del
Ecuador, CRM, INERHI, & CONADE, 1991). Precipitation follows a
roughly similar pattern to elevation, i.e. increasing from west to east.
Nonetheless, strong rains can fall in most of the territory and flooding is=
an
issue in many areas (=
Rossel, Goulven, Le, & Cadier, 1999; Rossel, Cadier, & Gomez, 1996). Regar=
ding
droughts, the plan has always been to convey water from the most humid area=
s in
the east to the driest land in the west. While having a variety of climates=
on
relatively such a small land area provides policy makers with more options;=
it
also makes water resource management more challenging for them.
The largest urban areas are in the center and west=
of
the province. Population is 1,369,780 and is currently growing at a rate of
1.6% (INEC, 2010). Much of the terr=
itory
is mountainous, and there are not many wide valleys in which flat land is
available for agriculture and urbanization. Nonetheless, agricultural and
livestock activities have taken place in the hills for many years; mainly in
the small hills but also in the lower parts of the larger mountains. Land u=
se
is continuously shifting between and towards economic land uses (Hernandez-Jimenez et
al., 2017; INEC et al., 201=
2),
what may place pressure on water resources management and natural disaster =
risk
management.
4.
SECTION 1: THE CLIMATIC CONDITIONS OF MANABÍ
What are the climates in Manabí?
To undertake an analysis of the provinces hydrolo=
gy,
a review of its climates is first carried out. For this purpose, different
sources of information are compared; among them: (i)
a climate report prepared by Pourrut (1994=
)
and the French institution of Development Research (IRD); (ii) the vegetati=
on
classification by Sierra (1999) (se=
e Fig.
1); (iii) the updated Köppen-Geiger climate map=
by Peel et =
al.
(2007) and Rubel & Kottek (2010=
)
(see Fig. 2a and 2b); and (iv) the climate map provided by the Ecuadorian
national meteorological and hydrological institution INAMHI (Moya, 2006) (see Fig. 2c). Note that INA=
MHIs
map is based on Thornthwaites worldwide
classification (Moya, 2006).
In the updated Köppen-=
Geiger
map by Peel et
al. (2007), several climates appear in Manabí province - some of
which would be expected in a tropical region: savannah (Aw), tropical monso=
on
(Am); some of which would be expected in a dry region: semi-arid hot (BSh) or arid hot desert (Bwh); as
well as others that are not expected for Manabí, since they correspond to
temperate climates: dry and warm summer (Csb), =
dry
winter and warm summer (Cwb), and without dry s=
eason
and warm summer Cfb). With exception of the
According to the Köppen-Geiger
map by Rubel & Kottek (2010), M=
anta
is located in the BSh
arid steppe hot (which might correspond to semi-arid), while Portoviejo i=
s in
the As equatorial savannah wi=
th dry
summer, Chone is in the Aw equatorial savannah with dry winter, and the northeastern
part of the province would correspond with the Am equatorial monsoon. However, note that this map locates the
main dam catchments within the savannah region. Errors of this type might be
expected due to the maps global focus and the coarse size of the pixels. On
the other hand, INAMHIs map has a better resolution and a more accurate
representation of the climates in the province.
According to INAMHI, the easternmost Manabí area, =
in
which part of the Daule Pe=
ripa
dam basin is located, has a B3 r A=
climate: warm, humid, with no or small water excess. Moving westwards, in=
the
areas of La Esperanza, Poza Honda, and the Río Grande catchment is the clim=
ate
classified as C2 s A: warm,
sub-humid, with moderate water deficit in dry season. Chone,
Calceta and part of Portoviejo fall within the =
C2 s2 A climate, meaning warm,
sub-humid with major water deficit in dry season. Most of Portoviejo falls
within the D =
d
A climate, which is warm, dry with no or small water excess. Finally=
, in
the westernmost part of Manabí, in Manta, climate is E d A which stands for warm, arid with no or small water exce=
ss.
Table 1 shows the meaning of each symbol on the INAMHI map. All figures were
produced in Geographical Information Systems using data from the sources
referred to above. Coordinates are projected local WGS84 17s format.
|
(a) |
|
|
(b) |
|
|
(c) |
|
|
Figure 1. Three main
classes of vegetation in Manabí (Source: Sierra,
1999): (a) Coastal dry shrubs in lowlands; (b) what is known as
savannah; and (c) evergreen mountainous forest. These are considered to
correspond with semi-arid, savannah and humid tropical climates,
respectively. |
|
(a) |
|
|
(b) |
|
|
(c) |
|
|
Figure 2. Main climates of Man=
abí
province. (a) and (b) are the climates according to the updated Köppen-Geiger map by Peel et
al. (2007) and Rubel & Ko=
ttek
(2010), respectively; (c) is the map presented by INAMHI (Moya, 2006) following the Thornthwaite classification. Notice that microclima=
tes
are not represented (left in blank) although they appear in the original
INAMHI map. All figures were produced in Geographical Information Systems
using data from the sources referred to above. Coordinates are projected =
local
WGS84 17s format. |
While the Thornthwaite
criteria are widely used and the INAMHI map is more accurate, Köppen is commonly applied primarily for educational
purposes (Peel et al., 2007) and it is, according to Kottek,
Grieser, Beck, Rudolf, & Rubel (2006), the =
most
frequently used source in climate classification. Perhaps this is because m=
any
of the names are straightforward to remember. Matching Köppen-Geiger
descriptions to a good extent, Sierra (199=
9)
presented a vegetation classification in which Manabí has areas with
mountainous humid tropical forest called Bosque siemp=
reverde
piemontano. Here, it is considered that this c=
ould
correspond with the Am climate class but also with a broader humid tropical
forest classification (including Af). For this study, names similar to=
the Köppen-Geiger map are adopted, and Manabí is consider=
ed to
have three main climates: Semi-Arid, corresponding with BSh;
Savannah, including both Aw and As; and Humid tr=
opical
for Am. Selecting these three climates allows for a rapid comparison and re=
view
of the literature generated throughout the world in similar climatic areas.=
According to Pour=
rut
(1994) the region around Manta may have less than 200 mm of rainfall=
per
year, most of it concentrated in the period December to April. According to=
Köppen-Geiger maps, this corresponds to the semi-arid=
and
arid climate. Moving eastward from the Pacific Ocean, between 200 and 400
mm/year is the mean rainfall around Portoviejo, located on the border betwe=
en
the drier Manta climate and the relatively more humid climate of the savann=
ah.
From Portoviejo, there is a marked transition in rainfall within few
kilometers. Two categories are found moving eastwards towards the Daule Peripa dam catchmen=
t.
Rainfall changes to a range of 400 to 1,300 mm/year in a region that includ=
es
the surroundings of Chone, and then from 1,300 =
to
3,000 mm/year in the Daule Peripa
catchment itself. This might correspond to a third category of climate (hum=
id
tropical) located further east, near to the boundaries with the Los Ríos, S=
anto
Domingo and Guayas provinces.
|
Table 1. Definition of INAMHI
climate map symbols (Source: Moya, 2006)=
. |
|
|
Water Regime
Index |
|
|
Symbol |
Definition |
|
A |
Super humid |
|
B3 |
Humid |
|
C2 |
Sub-humid |
|
D |
Dry |
|
E |
Arid |
|
Seasonal Wat=
er
Variation |
|
|
Symbol |
Definition |
|
r |
No or small water deficit |
|
s |
Moderate water deficit in dry season |
|
s2 |
Major water deficit in dry season |
|
W |
Moderated water excess in rainy season |
|
d |
No or small water excess |
|
Temperature
Regime |
|
|
Symbol |
Definition |
|
A |
Warm |
|
B4 |
Semi-warm or mild warm |
|
B3 |
Warm temperate |
|
B2 |
Cold temperate |
|
B1 |
Semi-cold or mild cold. |
The mean annual temperature ranges from 18 to 24
degrees Celsius. There is not a marked transition in the temperature observ=
ed
from east to west, but rather a difference between two categories: (1) the
hottest area near the coast and in the valleys, where Manta, Portoviejo and=
Chone are located, at around 24 degrees Celsius; and =
(2)
near 18 degrees Celsius in the mountainous areas where, for instance, Jipijapa is located.
5.
SECTION 2: CRITICAL SURVEY OF RELEVANT LITERATURE<=
/a>
Semi-arid hydrology
The hydrology of semi-arid regions differs
substantially from that of the more-studied temperate climates (Simmers, 2003). Rivers in those regions =
are
ephemeral and many hydrological processes are not continuous or non-linear,
whilst rivers in temperate regions tend to be perennial (García-Pintado, Barberá, Erena, & Castillo, 2009). Hortonian overland flow also known as infiltration e=
xcess
overland flow (IEOLF) is believed to have the greatest contribution to the
runoff in semi-arid regions, which is not the case in temperate regions
There are also other information gaps in terms of =
the
hydrology and geomorphology of semi-arid areas. For instance, the extent to
which IEOLF contributes to runoff in semi-arid regions has been challenged =
by
recent studies, such as that conducted by =
van
Schaik, Schnabel, & Jetten (2008) who found that subsurface
preferential flow takes place in semi-arid regions under certain
circumstances. Regarding the river geomorphology some authors found that ev=
ery
10 years a cross-section-changing event occurs (Bull
& Kirkby, 2002). However most of this research was conducted in a
region not directly influenced by El Nińo: i.e., Spain. Knowing the shape, a
river will take is essential for populations living near rivers, in terms of
their wellbeing and property insurance. Hydrology and geomorphology topics =
in
semi-arid regions therefore need further research.
While in temperate regions hydrological modelling =
is
used to analyze and understand hydrological processes, in semi-arid catchme=
nts
modelling is seldom applied since there are issues that not yet have been
solved or that have proved difficult to overcome. For instance, because many
hydrological processes are not continuous, runoff is complicated to measure=
and
study. In semi-arid catchments, the influence of transmission losses is
related to these discontinuities (Dunkerley
& Brown, 1999). Financial and logistics constraints may be two
additional reasons why semi-arid hydrological processes are less documented=
(Simmers, 2003). About logistics, researc=
h in
semi-arid regions run into difficulties with establishing monitoring networ=
ks.
This is partially because most significant rainfall events are very
heterogeneous in space and time. In addition, problems such as personal saf=
ety
and equipment robbery are common (Bull &am=
p;
Kirkby, 2002). Further, many measuring devices have been destroyed w=
hen
flooding occurs (Maneta, Schnabel, & J=
etten,
2008). In many cases, lack of knowledge in semi-arid regions does not
allow to accurately mimic river discharges by hydrological models, thus pla=
cing
constraints on the work of local practitioners.
There are several published studies that have
demonstrated the lack of accuracy when attempting rainfall-runoff modelling=
in
semi-arid and arid regions. Relevant model parameters are often not calibra=
ted
and high-quality data is generally not available. Neither is there any
agreement in the literature as to which models give better results: empiric=
al,
semi-empirical or the more complex distributed models (McIntyre & Al-Qurashi, 2009). For instance, a study carried
out in a catchment in Oman found poor prediction performance in most cases =
and
higher-than-expected uncertainty (Al-Qurashi, McIntyre, Wheater, & Unkrich, 2008).
Based on the experience of these authors, the effort of using complex model=
s is
not justified for semi-arid and arid regions. A study using 10 rainfall-run=
off
models (McIntyre & Al-Qurashi, 2009)
and a study in the US (Yatheendradas et al., 2008) also found po=
or
results and high uncertainties in rainfall-runoff modelling. Given that
hydrological modelling may not be accurate enough, hydraulic modelling shou=
ld
be considered as an option that could provide a good solution, or a
complimentary one.
Among all the literature on hydrology, the develop=
ment
of savannah climate hydrology is unique. Since it shows similarities with
semi-arid climates such as those found around the Mediterranean Sea many
authors have tried to extend the principles of the semi-arid hydrological
processes to savannah catchments. In a similar practice, literature from mo=
re
humid tropical river basin studies has been applied in savannah research
because savannahs are, by definition, located in the tropics (Smith & Smith, 2007). Those attempts
probably took place because of the lack of previous studies. Researchers tr=
ied
to use existing or available literature to guide/refine their research
questions, and/or to provide a framework for their research results.
Both semi-arid and savannah environments are
characterized by water scarcity and ephemeral rivers. The precipitation is
concentrated mostly or completely during a few months, while the rest of the
year there is a lack of rainfall (Smith &a=
mp;
Smith, 2007). Most savannah catchments are in developing countries, =
such
as those of sub-Saharan Africa, and South America, except for Australia. Th=
ese
countries still lack extensive monitoring networks for hydrometeorological =
data
collection (Petheram et al., 2012). In general, a backlog of hydrological
research exists in these regions. Nevertheless, few, yet important, efforts
have been made by institutions such as ORSTROM (now IRD) and SCIRO. They ha=
ve
formed much of the basis for the existing knowledge and outlined certain
research paths.
Despite the similarities between semi-arid and
savannah, a few important differences exist that ultimately affect the
hydrological processes. Farrick & Bran=
fireun
(2014), found that semi-arid vegetation species have a type of waxy
layer covering their leaves. This has not been found for savannah plants.
Furthermore, the crusting patterns found on semi-arid soils are not reporte=
d on
savannah soils. Both findings suggest an increase in the imperviousness of =
the
surface layers with which rainfall interacts in the first place. This has b=
een
called repellency, and Farrick (2014)
argues that frequent fires -which take place in semi-arid Mediterranean
regions- increase this property. The low density of vegetation cover in
semi-arid regions is also believed to be highly influential. Therefore,
interactions of rainfall with canopy and soil surface could be expected to =
lead
to different processes in terms of runoff production. Several studies have =
yet
to confirm these findings and, as such, they should be taken with caution.
Nevertheless, they raise awareness that differences between BSh
and Aw-As can exist and could have an influence on the hydrological process=
es,
and that more thorough research is needed. More attention from the scientif=
ic
community could lead to stronger conclusions.
Despite the notable contribution to the body of
knowledge by Australian authors, the applicability of their results could be
inappropriate for Manabí. Although certain soil characteristics could be
similar (Cook et al., 1998), swelling clays can be found in both
environments, there are also certain differences to consider. The slopes in=
the
Australian wet-dry tropics are reported to be generally low. In Manabís Aw=
-As
region, in contrast, the landscape is dominated by hills and valleys. Also,
Australias dry evergreen environments differ significantly from its decidu=
ous
or semi-deciduous counterparts from the Americas e.g., those in parts of
Mexico and Manabí (see Fig. 3). In Australia, forests are evergreen because=
of
soil infertility and the high cost of producing new leaves. Higher air
temperatures are believed to favor the growth of evergreen trees. In additi=
on,
the soil composition (coarse) and the soil depth (shallow), together with t=
he
geological setting, cause water to be retained in an area above the imperme=
able
layer, which can easily be reached by the evergreen tree roots (Bowman & Prior, 2005). In contrast, =
the
soils in the Manabí savannah region are deeper and more fertile, which may
explain the feasibility of yearly leaf production (Smith & Smith, 2007). For As-Aw areas, it has been shown t=
hat
having vegetation cover, even if only in patches, can obstruct runoff reduc=
ing
soil and water losses. Water infiltration in the soil is likely to increase=
(Bartley et al.,
2006). Because of these differences in land cover and canopy
interactions with rainfall, runoff in Manabí and Australia can vary
significantly.
Similar to the leaf and
crusting uncertainty, there is no strong comparison between BSh
and Aw-As in terms of connectivity and transmission losses. While there are
some findings on transmission losses from the semi-arid counterpart, someth=
ing
similar could occur in savannah catchments. One study compelling a signific=
ant
number of research concludes that, in some cases,
water losses are considerable (Dubreuil,=
1985).
In addition, the characteristics of the storms bringing rainfall to savannah
basins may be different from those of semi-arid basins. Surface runoff does=
not
occur with much frequency in Aw-As environments. Some savannah catchments
behave the same as temperate catchments in that specific thresholds of
antecedent water storage and rainfall amounts are found prior to the start =
of
runoff. Nonetheless, according to Farrick =
&
Branfireun (2013), these remain completely undescribed, both
empirically and conceptually, in tropical dry forest catchments.
|
|
|
(a) |
|
|
|
(b) |
|
|
To further complicate research activities, savannah
climates can have different names in different parts of the world, and local
researchers write their reports using those names. For instance, in Brazil =
and
in parts of South America they can be called Cerrado,
Caatinga, Llanos or Dry Chaco; while in Australia, they are referred to as
wet/dry tropics, or Dry Evergreen. It is curious that some Brazilian auth=
ors
have referred to their study areas simply as semi-arid (Montenegro & Ragab, 2010; de Araújo & G=
onzález,
2009). Perhaps this is done to place results in a wider context,
although it fails to consider the differences that can exist. Studies in Me=
xico
have referred to savannah catchment as dry tropical or tropical deciduou=
s
forests (Farrick & Branfireun, 2014; V=
ose
& Maass, 1999). Furthermore, many studies have been written in
French, Spanish or Portuguese, making them less visible for researchers from
the primarily English-writing hydrological community.
Another environment in which to seek out Aw-As
literature is in Sub-Saharan Africa. Findings there could provide interesti=
ng
insights into the hydrology of savannah environments in general. For instan=
ce,
in a study by Chevallier & Planchon (1=
993),
it was found that all the primary known runoff generating processes take pl=
ace
in a savannah river basin. These include variable source area, Hortonian Overland Flow (HOLF), Saturation Excess Ove=
rland
Flow (SEOLF), soil pipes, preferential flow, throughflow, and return flow.
Considering this, certain comparisons would be permissible.
Compared with its counterparts in temperate region=
s,
there is a sizable knowledge gap regarding the hydrology of humid tropics,
including the hydrology of tropical rainforest (TRF). In
particular, little is known about the potential changes in the evapo=
transpiration
and runoff generation patterns which might result from human activities in
these environments (Wohl et al., 2012). There is also a need to determine the
magnitudes of water fluxes and the residence times of water in the soil. Un=
til
today, it is
known that a large part of the key event processes take place in the soil a=
nd
in the forest canopy (Ward & Robinson, 2000).
With respect to the forest canopy, the layer can be
regarded as a water reservoir. The canopy has a capacity for interception a=
nd storage
of precipitation, either in the form of rain or mist (called horizontal
precipitation) (Cavelier & Goldstein, =
1989),
and plays a particularly important role in TRF. The canopy also has an
influence in/on the evapotranspiration processes (Wohl et al., 2012).
Individual canopy characteristics control the quantities and qualities of w=
ater
temporarily stored in this layer (Fleischb=
ein,
Wilcke, Valarezo, Zech, & Knoblich, 2006), as well as the quanti=
ties
and qualities of water that reach the soil through the branches, leaves and
stems; also called throughfall (Bruijnze=
el,
1990). Challenges to the measurement and quantification of water
movements through these layers exist.
Before the water reaches the ground, it may intera=
ct
with a layer of fallen leaves and branches accumulated on the grounds surf=
ace,
called the litter layer. This layer can be considered a small reservoir that
gradually releases water during the dry season. However, there are
uncertainties regarding litter hydrology of TRF with respect to the water
holding capacity and the drainage rate. Most of the available literature is
based on studies in regions with temperate climates. An interesting finding=
by Li, Niu, & Xie (2014) is that the lit=
ter
layer reduces the runoff volume, produces a lag in the onset of runoff, and
minimizes soil loss. In a tropical region, Park,
Friesen, & Serrud (2010) carried out data collection and analysi=
s in
a setting with primarily commercial species that might not be found in Mana=
bí.
In many temperate and tropical regions, the accumulation of leaves might not
occur in the same way as it does in Manabís humid forests, which probably =
is
due to the differences in tree species.
While the forest canopy and the litter layer can h=
ave
the function of protecting the soil from erosive processes, it can also ham=
per
the generation of runoff as infiltration excess overland flow (Shaw, Beven, Chappel, & Lamb, 2010).=
Hortonian flow is often believed to have little relev=
ance
in forest environments, including humid tropical trees (Ward & Robinson, 2000), although its occurrence has been s=
een
in association with steep slopes where natural vegetation has been cut,
exposing the shallow soil (Campling, Gobin,
Beven, & Feyen, 2002). However, there is still not enough litera=
ture
or evidence to support the current state of knowledge. In fact, Bruijnzeel (2001) and Wohl et al. (2012)
suggest that one of the most important knowledge gaps are the effects of the
deforestation of tropical forests. All this invites us to carry out researc=
h in
fields where there are still processes to be understood.
The precipitation that has not been retained in the
canopy layer, or in the litter layer, infiltrates. The interactions of wate=
r in
the soil are diverse since, hydrologically speaking, there are many paths t=
hat
the water can take (Ward & Robinson, 2=
000).
Quantities of water can remain in the organic horizons (A, B and h) and ret=
urn
to the surface in short periods of time. Other quantities can penetrate tow=
ards
the C horizon and return to the surface in longer periods of time and in
geographic locations very distant from the initial location (Shaw et=
al.,
2010). These interactions are in turn related to other runoff genera=
tion
mechanisms, including the saturation excess overland flow (SEOF) and flow
through natural pipes or pipes (Chappe=
ll,
2010). With respect to natural pipelines in TRF soils, there are sti=
ll
gaps in knowledge, justifying more in-depth studies about the true influenc=
e of
the flows by natural pipes. According to Chappell (2010) it is necessary to
quantify the lengths and dimensions of natural pipe networks and the
mechanisms recharging these pipe networks.
Compared to the number of publications from temper=
ate
regions, few studies have been conducted in tropical humid areas around the
globe. However, the experiences of Kinner =
&
Stallard (2004), Campling et al. (2002), and Molicova, Grimaldi, Bonell, & Hubert (1997)<=
/span>
are illustrative for good practice. In their studies, from different region=
s of
the globe, they used hydrological modeling to determine the processes of ru=
noff
generation. Similarly, Chappell, Franks, &=
amp;
Larenus (1998) used hydrological modeling to determine soil properti=
es
that influence the runoff generation processes.
Regarding research on the hydrology of tropical hu=
mid
forests in Ecuador, to the authors knowledge, thus far studies have primar=
ily been located in the eastern and western Andes mountain=
range
(e.g. Fleischbein et al., 2006; Boy, Vala=
rezo,
& Wilcke, 2008; Crespo et al.,
2012; Goller et al., 2005).
However, for Manabí, no studies have been found that attempt to describe or
analyze the hydrological processes of tropical humid forests, let alone whi=
ch
attempt to specifically understand the processes of runoff generation. It is
hereby recommended that studies on these topics be carried out.
For this study, names similar to the
There is
literature available for use in Manabís semi-arid region. Significant prog=
ress
has been made elsewhere, mostly in Mediterranean areas. Since there might be
differences between semi-arid Mediterranean catchments and Manabí BSh catchments mostly in the soil and vegetation spe=
cies
more research is needed to determine whether these findings could be applie=
d in
Manabís semi-arid region. Perhaps the main issue to be tackled are the
difficulties faced in the establishment of monitoring networks. Rainfall
satellite data and remote sensing technologies should be employed where
possible. Given that hydrological modelling may not be accurate enough,
hydraulic modelling should be considered as an option that could provide a =
good
solution, or a complementary solution, in obtaining flow rate data.
Nonetheless, rainfall-runoff modelling is not discouraged. Some efforts cou=
ld
be made in Manabí before this option is discarded.
For the savann=
ah
region of Manabí, there are also many gaps to be filled. Here a call for
caution is necessary, as many authors have tried to extend the principles of
the semi-arid and humid tropical hydrological processes to savannah catchme=
nts.
On the other hand, while some savannah literature from other regions such =
as Africa
and México could be of use, given the differences outlined in the manuscri=
pt,
findings in Australia might have their limitations. Perhaps the main point =
to
investigate is whether Manabí semi-arid vegetation and soils have
characteristics different than the Manabí savannah counterparts, which could
lead to an increase in the imperviousness of the catchments. Here it is agr=
eed
with other authors that researchers should adopt one name for their findings
regarding savannah climates, rather than reporting with different names suc=
h as
cerrado or caatinga.
Regarding Mana=
bís
humid tropic hydrology, including tropical rainforest (TRF), there is a gro=
wing
body of knowledge emerging from similar regions elsewhere around the globe
which could be of use here. Nonetheless, given the potential differences
between tree and shrub species found in Manabí and those found elsewhere,
studies in Manabí must be carried out. Given the strong seasonality of rain=
fall
in Manabí and the orographic effect, it is believed that many of Manabís T=
RF
remain green because of the interception from clouds and mist in the
mountainous areas. Attention should thus be given to the interception of wa=
ter
from mist and clouds together, especially in the quantification of this
interception. Finally, given the land use change, another important area of
focus is the effects on the dry season flow or on the total amount of water
that may arise not only because of the deforestation of tropical forests, b=
ut
also of their deciduous dry counterparts.
Thanks to havi=
ng
three climates in a relatively small region, Manabí could be regarded as a
laboratory for hydrological research. It is evident that findings obtained =
in
Manabí could also be applied to other regions with similar characteristics.=
Some ideas presented in this manuscript are also f=
ound
in the authors M.Sc. dissertation at the University of Leeds, UK. The auth=
or
would like to thank M. Zamora and L. Reyna for their constructive comments =
on
the late stages of the manuscript and to R. Cusme and
M. Alcivar for providing support with the image=
s.
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Vol. 9, No. 2, 2018
Revista
semestral de la DIUC =
=
81=