Climate Change Effects on Regional Watershed
Global Climate Change
Evidence from around the world indicates that global climate change is causing weather incongruities which are outside the range of what can be considered “normal weather anomalies.”
- The melting of glaciers in Alaska, Argentina and the Himalayas has considerably reduced the yearly snow pack stored in them and has caused flooding in the winter and low flows of water currents in the summer.
- The shifting of yearly rains in many countries from normal patterns to random events characterized by strong thunder storms that unload several inches of rain in a matter of hours. These storms are usually followed by long periods without a drop of rain therefore leading to drought.
- The thawing of permafrost regions in Alaska and Siberia softens the ground and makes large trees fall over.
In light of the above, authorities and society of the State of Guanajuato, located in the geographic center of Mexico about 220 miles northwest of Mexico City, are deeply concerned about the impacts which the global climate change is going to have on their State.
Over the last 20 years Guanajuato has been adding sectors to its productive base such as the manufacture of automobiles and auto parts. Also, some of the older sectors like footwear manufacturing and leather processing have been modernized. Nevertheless, agricultural production is still the largest single productive activity in Guanajuato as measured in terms of employment and gross value generated. (Although the car industry has a higher gross value, only part of it stays in Guanajuato.) And most significantly, agricultural production utilizes 87% of all surface and underground available water in Guanajuato.
Objectives of the Present Study
The present study has as its objectives:
- to examine past and present climatology of the various regions of Guanajuato in search of evidence that shows how the climate is changing,
- with this knowledge, to focus on the specific climate effects that are present in each region,
- to examine the natural and man-made processes in each region and to determine how they may be impacted by the effects of the climate change, and
- to propose policies and mechanisms that will lead to actions of mitigation or actions of adaptation to the new climate conditions.
The majority of climate change studies focus on the use of General Circulation Models (GCMs) of the world’s atmosphere that have been created to test the effect of increased carbon dioxide accumulation over time. The results of these models are given in a time scale measured in decades and a geographic scale measured by whole regions of the world.
The purpose of the GCMs, and the carbon dioxide scenarios that they generate, has been to provide awareness to high level country executives – presidents, prime ministers and the like – of the expected impacts of climate change in the various regions of the world. They have been utilized in support of the negotiation process of world climate forums like the recent COP16 in Cancún, México.
As well as supporting high level negotiations, the carbon dioxide scenarios have also been employed by individual countries to ascertain the impacts they can expect from the climate change in the long run. Using the knowledge in these analyses some of the countries are designing programs to counter act the effects of climate change.
Mexico is one of the countries that has already been engaged in several studies that utilize GCMs such as Geophysical Fluid Dynamics Laboratory Model (GFDL-R30), from NOAA; the Canadian Climate Model (CCC), from the Canadian Climate Center and the Modelo Termodinámico de la Atmósfera of the National University of México (UNAM) [Magaña, 1997]. From the global scenarios generated by the above models, and utilizing stochastic and statistical methodologies such as the Long Ashton Research Station-Weather Generator (LARS-WG) and the Statistical Down Scaling Model (SDSM), the Mexican researchers have scaled down the global results to apply to the geography of Mexico and to specific regions within Mexico.
The Context of the Foresight Scenarios of Guanajuato
Today, the probably competing concerns in one of Guanajuato’s watersheds are related to the following questions:
- Will there be enough irrigation water to finish the agricultural cycle that has been started?
- Will there be enough rainfall to extend the quantity of potable water stored beyond the next six months?
These short time scale problems for small geographic areas cannot be solved using the scaled down results of GCMs since this leads to a “top-to-bottom” approach [UNFCCC, 2006] which is not always directed towards the needs of the region under study and can result in uncertainty regarding the climate projection (e.g. what would it happen if the CO2 contents in the atmosphere is not twofold in volume for the 2025 – 2050 period as had been assumed).
What is needed in Guanajuato instead is a “bottom-to-top” approach that begins by considering that “climate change will affect the rain-runoff process”. This statement has been considered to be the “stepping stone” [UNFCCC, 2006] for understanding and anticipating climate change for the following reasons:
- In years to come rain will be abundant but, in contrast to “normal patterns,” it will rain in short periods of strong precipitation that will be followed by long period without rain.
- Temperature in the next decades will increase between 1.5 and 3.0 degrees centigrade above the norm resulting in more evaporation from land and sea that will feed strong downpours.
In addition, since the concerns of the people from Guanajuato are the problems of specific regions within the state that extend from present day to 20 or 25 years into the future, the context that emerges unsurprisingly supports a “bottom-to-top” examination which:
- considers all processes that will be impacted by the changes in rain-runoff,
- identifies the impact of the vulnerabilities of these processes, and
- permits that policies and mechanisms of mitigation and adaptation to new climate condition can be devised and then instrumented.
Also, because the “bottoms-to-top” approach is anchored in the present, the “initial boundary” conditions for the foresight scenario process are known for each watershed of the State. The water cycle parameters (precipitation, temperature and evaporation) are known. The parameters of man-made processes (population, productive activities outputs, etc.) are also known. Through the planning process trajectories for future expansion have already been created. The only remaining question is what would be the “terminal boundary” conditions of the climate variables in Mexico in 2030?
Scenarios of CO2 in Mexico
The first step is to consider the expected global environment in 2030. Unless large contributors of greenhouse gases like the U.S., China, and the European Union agree to drastically reduce their emissions in the near future, the realization of a global scenario in which the contents of CO2 in the atmosphere will have doubled by the period 2025-2050 is very likely. When this happens the State of Guanajuato and the rest of the world need to have developed policies and mechanisms that will enable them to adapt to the new climatology.
Since we are assuming that this global scenario will emerge, the task in hand is to obtain from the global scenario for Mexico and preferably for the region of the State of Guanajuato, temperature, precipitation and evaporation for 2030.
Among the global climate change studies developed in Mexico there is one entitled [Maderey, 2000], “Los Recursos Hidrológicos del Centro de México Ante un Cambio Climático Global,” of Laura E. Maderey and Arturo Jiménez in which the scale reduction of three GCMs is performed for the Lerma River Basin. Since 50% of the area of this basin is within the boundaries of State of Guanajuato the values of temperature, precipitation and evaporation from this study provide the necessary terminal boundary for the foresight scenarios of Guanajuato.
Foresight Scenarios Generation
Having set the initial and terminal boundaries for the climate variables we proceed to build the construct which will generate the foresight scenarios of the State of Guanajuato that is made up of two elements:
- The Atmospheric Interface generates the:
- daily rain patterns that mimic the expected short bursts of powerful storms that would be followed by dry weather of the expected climate change and
- daily temperature and evaporation patterns with upward tendencies as they are also expected in the future.
- ProEstado/MAUA/Clima®, (MAUA), is a Dynamics model that utilizes as inputs the meteorological variables from the Atmospheric Interface for each of the 13 watershed into which the State of Guanajuato has been broken down. That result from the implementation of policies over an extended period of time.
Description of the Construct Elements
- Atmospheric Interface
Two distinct scenarios have been prepared and tested with MAUA to evaluate the impacts of climate change. The first scenario assumes that for the simulation horizon of 31 years there are no effects of climate change. This Base Scenario, which is being used as a base of comparison, requires daily precipitation time series from November 1st, 1999 until October 31st, 2030. For each of the 13 watersheds of the State synthetic time series (Base Series) have been developed by the repetition of a “normal pattern” of precipitation for the period 1999-2008. This “normal pattern” was defined as the rain pattern that exists between two maximum rain events.
For the Climate Change Scenario, considering that extreme events will be intensified in magnitude and frequency, the periods between atypical extreme maximum events were selected. After that, the selected periods were reduced by 50% which is equivalent to doubling the frequency.
A further step included the selection among the atypical maxima, the year with the maximum-maximorum. The same was done for atypical minima and both the maximum-maximorum and minimum-minimorum atypical extremes were inserted in the Base Series.
These heuristic procedures to create synthetic daily time series of rain seem to be corroborated by an additional analysis performed for the 2010 decade in which drastic reductions in precipitation for various zones of Guanajuato were found.
MAUA is a dynamic model built on theory, information, knowledge and data [Huerta, 2001]. It is also built on first-hand field visits to establish the “Ground Truth”; that is, which systemic elements to be modeled – whether natural or man-made – exist on the terrain. See the DESCRIPTION OF ProEstado-MAUA
MAUA breaks down the state of Guanajuato into three major rivers’ basins.
- the Lerma River Basin in the southern part of the State has 10 sub-watersheds;
- the Northeast Basin has two watersheds – the Laguna Seca which is a closed watershed and the Pánuco River which is the beginning of one of Mexico’s largest rivers whose waters flow into the Gulf of Mexico and,
- the Northwest Basin that is the Verde River Basin.
Foresight Climate Change Scenarios for Guanajuato
The results of the simulation of the Base and Climate Change Scenarios are presented for the Solis Dam which regulates the Lerma River Basin in Guanajuato. The Turbio-Palote watershed, which is part of the Lerma River Basin, has been selected as an example because it has a varied productive activities and the largest human settlement in the State of Guanajuato. Of course, the other 12 watersheds of Guanajuato are also part of the integrated model..
The Simulation Horizon extends from November 1st of 1999 to October 31st of 2030. From November 1st of 1999 to October 31st of 2004 was the period used to calibrate the model for a previous project. From November 1st of 2004 to October 31st of 2007 was the period to recalibrate the model for the present project. Beginning November 1st of 2007 to October 31st of 2030 is the scenario horizon. (For additional information see the paper: A System Dynamics Approach to Examine Climate Change Impacts: The Case of the State of Guanajuato, México,”)