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Water, Environment and Climate Change © Universidad de las Américas, Puebla 2009
Possible Scenarios of Global Climate Change Effects on Potential
Evaporation in the Watershed of the Rio Conchos, Mexico
Jose A. Raynal-Villasenor
Department of Civil and Environmental Engineering
Universidad de las Americas, Puebla,
72820 Cholula, Puebla, Mexico
Tel.: (52-222) 229-2647
josea.raynal@udlap.mx
J. Alfredo Rodriguez-Pineda
World Wildlife Fund-Desierto Chihuahuense
Coronado # 1015, 31000 Chihuahua, Chih. México
Tel.: (52-614) 415-7526
alrodriguez@wwfmex.org
Abstract
The Conchos River Basin is the largest watershed for the northern state of Chihuahua, Mexico,
and the main surface water source for the Rio Grande Basin. The Rio Grande is also the physical
border between Mexico and the United States of America, from El Paso-Ciudad Juarez down to
Brownsville-Matamoros. Due to the international importance of this hydrological basin this work
focus on the construction of potential climate change scenarios and its effects on the evapo-
transpiration and moisture deficits. Besides, we construct likely scenarios that could help to
define an integrated watershed management to mitigate those global climate change impacts in a
basin already affected by recurrent drought periods.
The results of this study, sponsored by the alliance between WWF-Fundacion Gonzalo Rio
Arronte, are presented here. The study methodology includes the selection of three representative
meteorological stations strategically distributed in the basin and with, at least, 30 years of
continuous climatic daily data. Besides, we selected prediction data from the Hadley Centre
(Hadley Centre, 2005) with respect the changes of surface air temperature and annual rainfall
generated by the global climatic change by the end of the XXI Century.
The results show that air temperature increment of 1 °C increases evapo-transpiration values
between 2.1 and 2.6% with respect current values. As a consequence, moisture deficit increases
from 2.4 to 3.38%. For air temperature increment of 2 °C, evapo-transpiration increases between
4.2 and 4.9% with respect current values and increment from 4.77 to 6.30% in soil moisture
deficiency. Finally, with an air temperature increment of 3 °C, the potential evapo-transpiration
increases between 6.4 and 7.5%, also increasing soil moisture deficit from 7.16 up to 9.64%.
It is expected that the insignificant annual rainfall increment in the basin with respect current
present values, will generate a negligible contribution for the potential evapo-transpiration
reduction in the Rio Conchos watershed. These scenarios conclude that immediate actions need
to be taken to mitigate climate change impacts all along the basin to mitigate such likely results.
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Water, Environment and Climate Change © Universidad de las Américas, Puebla 2009
Keywords: Climate change, evapo-transpiration, moisture deficit, short grass, open water
Introduction
Global climate change has started to be accepted as a major threat to mankind survival during the
next years including the next century. The Intergovermental Panel on Climate Change (IPPC) has
been leading the efforts of dissemination the global climate change research results through their
periodical reports being the first one the IPCC First Assessment Report (1990) and the latest the
Fourth IPCC Assessment Report (2007). Right now, the Fifth Assessment Report is in progress
and will be completed the year 2014.
The Hadley Centre has been forecasting, world wide, the increment of climate related parameters
such as surface air temperature, precipitation, soil moisture content, sea level change, sea-ice
area, and sea-ice volume since many years back. This paper is focused on the evolution of the
first three climatic parameters (Figures 1, 2 and 3).
The Conchos River has a large impact on the Rio Grande hydrological system as the main water
provider, observe the light gray area in figure 4. Moreover, for the northern state of Chihuahua,
Texas and northeast Mexico, the surface water resources from this international basin have a
large impact on social, economic activities and nature conservancy. Therefore, it was needed to
construct potential scenarios of the global climate change, with regard to evapotranspiration and
moisture deficit, to provide scientific evidence for the policy makers that will help them to define
an integrated watershed management to help mitigate the climate change expected impacts.
Figure 1 Forecast for the change in annual average surface air temperature
(Hadley Centre, 2005)
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Water, Environment and Climate Change © Universidad de las Américas, Puebla 2009
Figure 2 Forecast for the change in annual average precipitation
(Hadley Centre, 2005)
Figure 3 Forecast for the change in annual average soil moisture content
(Hadley Centre, 2005)
189
Water, Environment and Climate Change © Universidad de las Américas, Puebla 2009
Figure 4 Main watersheds in the state of Chihuahua, Mexico
Main Objective
The main objective of this study is to define the potential scenarios of the global climate change
impact, now in course, upon the evapo-transpiration and soil moisture deficit in the Conchos
River Basin, considering two specific surfaces: water and short grass.
Methodology
Penman`s equation is the main tool applied for this climate study (Steward and Roberts, 1984):
()
()}
()
⎭
⎬
⎫
⎩
⎨
⎧
−
⎟
⎠
⎞
⎜
⎝
⎛
+
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
+∆
∆
−
+−
⎩
⎨
⎧
⎟
⎠
⎞
⎜
⎝
⎛
+−
⎟
⎠
⎞
⎜
⎝
⎛
+−
+∆
∆
=
ee
U
e
N
n
T
N
n
albRE
s
a
160
0.126.01
044.034.0
9.0
1.0
5.0
25.01
4
γ
σ
γ
(1)
190
Water, Environment and Climate Change © Universidad de las Américas, Puebla 2009
where:
E = evaporation (mm/day)
∆ = slope of the saturated vapor pressure curve (mb/°C)
Ra = incoming radiation at the top of the atmosphere (mm/day)
n = actual number of sunshine hours (hours)
N = maximum number of sunshine hours (hours)
σT4 = surface back-radiation emitted by a surface at temperature T (mm/day)
T = mean daily temperature (°C) ; U = daily wind run (km/day)
e = mid-morning vapor pressure (mb) ; es (T) = saturated vapor pressure at temperature T (mb)
γ = psycrometric constant ( 0.67 mb/°C)
Equation (1) was applied to surface water and short grass soil covers, for all potential scenarios
of air temperature and annual rainfall increments.
Discussion of Results
Using the air temperature increments data base forecasted by the Hadley Centre (2005), and
including the results presented during the IPCC’s Fourth Assessment Report (IPCC, 2007), this
paper reports the likely scenarios for global climate change impacts on evapo-transpiration and
soil moisture deficits for the Conchos River Basin in northern Mexico.
The results obtained show that for an increment of air temperature of 1 °C, the values of potential
evapotranspiration will rise from 2.1 to 2.6% with respect the actual values, see figures 5, 6, 9,
10, 13 y 14. As a direct consequence of these results, the moisture deficit will rise up from 2.4 to
2.6 % with respect the current values, see figures 7, 8, 11, 12, 15 y 16.
With an increment of air temperature of 2 °C, the values of evapotranspiration will rise from 4.2
to 4.9 % above actual values, see figures 5, 6, 9, 10, 13 y 14. For this case, the soil moisture
deficit will rise from 4.8 to 6.3 % with respect the current values, see figures 7, 8, 11, 12, 15 y 16.
Finally, for an increment of air temperature of 3 °C, the values of evapotranspiration will rise
from 6.5 to 9.6 % with respect the current values, see figures 5, 6, 9, 10, 13 y 14. In this case, the
soil moisture deficit will rise from 7.2 to 9.6 % with respect the current values, see figures 7, 8,
11, 12, 15 y 16.
The forecasted increase in annual precipitation for this region of Mexico has a negligible
influence with respect to the moisture deficit, see figures 7, 8, 11, 12, 15 y 16.
An interesting feature is observed at the results shown before, the more pronounced changes in
evapo-transpiration and soil moisture deficit are those of meteorological station at Parral, where
the climate is more humid and temperatures are cooler than the other two selected meteorological
stations in this study, the least pronounced results were those obtained for meteorological station
Ojinaga, which has the basin driest climate and the hottest temperatures.
191
Water, Environment and Climate Change © Universidad de las Américas, Puebla 2009
Conclusions
Based in the results obtained in this study, there will be an important increase for values of
evapotranspiration and soil moisture deficit at the Conchos River Basin, Mexico, generated by
those results forecasted for this arid region of Mexico.
These results are a voice of warning for the development of economic activities in the Conchos
River Basin, like current agriculture practices and water resources management without
considering a holistic approach. The water demands for agriculture will increase up to 10 % for
the worst case scenario, just to cover the soil moisture deficit increment produced by the rise of
air temperature. In addition, an increment of about 10 %, in the worst case scenario, for surface
water evaporation, will produce a reduction of about 10 % on stored volumes at dams and lakes
due to the evaporation increments from surface water by effects of air temperature increments up
to 3 °C.
The Conchos River will face a combined water scarcity of up to 20 % in the following years as a
consequence of the air temperature increment produced by the global climate change.
These results conclude that immediate actions need to be taken to mitigate climate change
impacts all along the watershed. WWF-CH (2007).
Acknowledgements
The authors express their deepest gratitude to the Alianza WWF-Fundacion Gonzalo Rio Arronte
for the support provided for the realization of this study and to the Universidad de las Americas,
Puebla for the means that made possible the publication of this paper.
References
Hadley Centre (2005). Climate Change and the Greenhouse Effect.
http://www.metoffice.gov.uk/research/hadleycentre/pubs/brochures/2005/climate_greenhouse.pd
f
Instituto Nacional de Estadística, Geografía e Informática (INEGI) (2008) Aspectos
Geográficos de Chihuahua, Climas.
http://mapserver.inegi.gob.mx/geografia/espanol/estados/chih/climas2.cfm?c=1210&e=08&CFI
D=2424453&CFTOKEN=27040706
Intergovermental Panel on Climatic Change (IPCC) (2007). Climatic Change 2007, Fourth
Report,
http://www.ipcc.ch/ipccreports/index.htm
Steward, J. B. y Roberts, J. M. (1984), Evapotranspiration, Chapter 9, Lecture Notes of the
Course on Estimation of Hydrological Variables, Institute of Hydrology, Wallingford, U. K.
World Wildlife Fund-Desierto Chihuahuense (WWF-DCH) (2007). Análisis Estocástico de
valores extremos de precipitación y caudal y afectaciones por cambio climático en la cuenca del
río Conchos, Estado de Chihuahua. Reporte Final.
192
Water, Environment and Climate Change © Universidad de las Américas, Puebla 2009
Potential Evaporation
Meteorological Station Ojinaga, Mexico
3375
3044
3449
3113
3523
3182
3595
3250
2000
3000
4000
12
Water Short Grass
Potential Evaporation (mm/yr)
Actual Conditions
1°C Increment
2°C Increment
3°C Increment
Figure 5 Evolution of potential evaporation in meteorological station Ojinaga, Mexico
(water and short grass)
Increase in Potential Evaporation
Meteorological Station Ojinaga, Mexico
(Water and Short Grass)
2.2
2.3
4.4
4.5
6.5
6.8
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
12
Water Short Grass
Increase in Potential
Evaporation (%)
1°C Increment
2°C Increment
3°C Increment
Figure 6 Increase in potential evaporation in meteorological station Ojinaga, Mexico
(water and short grass)
193
Water, Environment and Climate Change © Universidad de las Américas, Puebla 2009
Increase in Moisture Deficit
Meteorological Station Ojinaga, Mexico
(Water)
0 -0.09
-0.42
2.40 2.40
2.41
4.80 4.81
4.82
7.16
7.16
7.19
Scenarios of Annual Precipitation Increase
Increase in Mositure Deficit
(%)
3°C Increment
2°C Increment
1°C Increment
Actual Conditions
Figure 7 Increase in moisture deficit in meteorological station Ojinaga, Mexico
(water)
Increase in Moisture Deficit
Meteorological Station Ojinaga, Mexico
(Short Grass)
0 -0.10
-0.47
2.51 2.51
2.52
5.04 5.04
5.06
7.51
7.51
7.54
Scenarios of Annual Precipitation Increase
Increase in Moisture Defict
(%)
3°C Increment
2°C Increment
1°C Increment
Actual Conditions
Figure 8 Increase in moisture deficit in meteorological station Ojinaga, Mexico (short grass)
194
Water, Environment and Climate Change © Universidad de las Américas, Puebla 2009
Potential Evaporation
Meteorological Station La Boquilla, Mexico
2540
2210
2593
2258
2645
2306
2702
2358
0
500
1000
1500
2000
2500
3000
12
Water Short Grass
Potential Evaporation (mm/yr)
Actual Conditions
1°C Increment
2°C Increment
3°C Increment
Figure 9 Evolution of potential evaporation in meteorological station La Boquilla, Mexico
(water and short grass)
Increase in Potential Evaporation
Meteorological Station La Boquilla, Mexico
(Water and Short Grass)
2.1
2.2
4.2
4.3
6.4
6.7
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
12
Water Short Grass
Increase in Potential
Evaporation (%)
1°C Increment
3°C Increment
3°C Increment
Figure 10 Increase in potential evaporation in meteorological station La Boquilla, Mexico
(water and short grass)
195
Water, Environment and Climate Change © Universidad de las Américas, Puebla 2009
Increase in Moisture Deficit
Meteorological Station La Boquilla, Mexico
(Water)
0
-0.23
-0.81
2.40 2.40
2.42
4.77 4.78
4.81
7.35
7.37
7.41
Scenarios of Annual Precipitation Increase
Increase in Moisture Defict (%)
3°C Increment
2°C Increment
1°C Increment
Actual Conditions
Figure 11 Increase in moisture deficit in meteorological station La Boquilla, Mexico
(water)
Increase in Moisture Deficit
Meteorological Station La Boquilla, Mexico
(Short Grass)
0
-0.28
-0.96
2.55
2.56 2.57
5.08
5.09
5.13
7.84
7.86
7.91
Scenarios of Annual Precipitation Increase
Increase in Moisture Defict
(%)
3°C Increment
2°C Increment
1°C Increment
Actual Conditions
Figure 12 Increase in moisture deficit in meteorological station La Boquilla, Mexico
(short grass)
196
Water, Environment and Climate Change © Universidad de las Américas, Puebla 2009
Potential Evaporation
Meteorological Station Parral, Mexico
2889
2522
2963
2588
3026
2646
3098
2712
0
500
1000
1500
2000
2500
3000
3500
12
Water Short Grass
Potential Evaporation
(mm/yr)
Actual Conditions
1°C Increment
2°C Increment
3°C Increment
Figure 13 Evolution of potential evaporation in meteorological station Parral, Mexico
(water and short grass)
Increase in Potential Evaporation Meteorological
Station Parral, Mexico (Water and Short Grass)
2.5
2.6
4.7
4.9
7.2
7.5
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
12
Water Short Grass
Increase in Potential
Evaporation (%)
1°C Inc re me nt
2°C Increment
3°C Increment
Figure 14 Increase in potential evaporation in meteorological station Parral, Mexico
(water and short grass)
197
Water, Environm
ent and Climate Change © Universidad de las Américas, Puebla 2009
Increase in Moisture Deficit
Meteorological Station Parral, Mexico
(Water)
0
-0.32
-1.02
3.11
3.12 3.14
5.81
5.83
5.87
8.87
8.90
8.97
ease
n Moisture Defict
(%)
Scenarios of Annual Precipitation Incr
Increase i
3°C Increment
2°C Increment
1°C Increment
Actual Conditions
tion Parral, Mexico Figure 15 Increase in moisture deficit in meteorological sta
(water)
Increase in Moisture Deficit
Meteorological Station Parral, Mexico
(Short Grass)
0
-0.38
-1.20
3.34 3.36
3.38
6.23
6.25
6.30
9.53
9.56
9.64
Scenarios of Annual Precipitation Increase
Increase in Moisture Defict
(%)
3°C Increment
2°C Increment
1°C Increment
Actual Conditions
Figure 16 Increase in moisture deficit in meteorological station Parral, Mexico
(short grass)
198
