Methodology of Guatemala NCAP Project

Submitted by Sukaina Bharwani 25th March 2011 19:17

Analytical Framework

The PNCC was aware that the following organizations were active in these policy dialogues. Guatemala's Agriculture Ministry (MAGA), Guatemala's National Forestry Institute (INAB), Guatemala's National Disaster Planning Network (CONRED)

Working through agents in these organizations, research was conducted in the Rio Naranjo and Rio San Jose/Rio Shutaque systems in order to identify an appropriate audience for the water management adaptation analysis that was planned for the NCAP project, which would follow the analytical process illustrated below. The basic structure of this framework is a four step process:

  • Step 1: Understand the implications of the general circulation models (GCM) of the global climate system for the climate in a particular region of the world.
  • Step 2: Deploy appropriate techniques to downscale possible regional climatic predictions to climatic time series representative of possible future conditions in watershed areas of interest.
  • Step 3: Evaluate how changes in the climate in these watershed areas will alter the local terrestrial components of the hydrological cycle, in particular streamflow, aquifer recharge and evaporative water demand, which are the types of flow that are typically managed.
  • Step 4: Assess how water systems dependent on these flows will perform under anticipated patterns of change, and evaluate management options to ensure the long-term performance of the water system in the face of these changes.

Hydrological Models

In order to implement the analytical framework shown in figure 5, models of the Rio Naranjo and Rio San Jose/Rio Shutaque systems needed to be constructed. These models run using future climatic time series constructed based on output from the GCMs, they assess how hydrological processes in the target watershed areas will change under alternative future climatic conditions, and they simulate the performance of the installed water management system under this future hydrological regime. In order to construct the required models, the PNCC selected the Water Evaluation and Planning (WEAP) system developed by the Stockholm Environment Institute (SEI) as a modeling platform.

The WEAP platform is a graphical software system in which a user assembles a series of model objects corresponding to the physical elements of a water system such as watershed areas, rivers, aquifers, reservoirs, diversion works and transmission links. These objects are characterized based on relevant available data. The WEAP user then defines a policy context, including the priority assigned to different water uses, the preferences between various supplies, and required flows in rivers and streams, within which the physical elements are arranged. This is done over a past time period so that the model can be calibrated to ensure that it provides a reasonable representation of the water system in question. The WEAP can then be used to construct “what if” scenarios about the future whereby critical system elements are varied. As an example, consider the following
sequence of scenarios relevant to investigating water sector adaptation to climate change:

1.  Current climate, watershed area conditions, infrastructure, and operating rules continue into the
future in the face of increasing water demand.
2.  In addition to increasing water demand, hotter and drier climatic conditions will change water-
shed area conditions, while infrastructure and operating rules continue.
3.  In the face of these change, efforts are made to:
a.  Rehabilitate degraded watershed areas; and/or
b.  Change rules governing the operation of the current infrastructure, and/or
c.  Add new infrastructure.

Scenario 1 is classic water planning, scenario 2 is a climate change impact assessment, and scenario 3 is a climate change adaptation study. Work with the WEAP in Guatemala has moved through each of these steps.

Data and Calibration

The PNCC collected the necessary streamflow, climatic, geographical and land-use data for the two chosen catchments. Having developed WEAP applications for the two catchments, the models were then calibrated so that modelled streamflow was a reasonable match to gauged values.

Climate Scenarios and Analysis of Impacts

There is still a great deal of scientific debate regarding the best methodology for transforming the information from the GCMs into something that can be used to carry out rainfall-runoff analysis at the watershed area scale. The PNCC chose to implement a “book-ending” approach whereby information from both pessimistic and optimistic GCMs was transformed for use in the Rio Naranjo and Rio San Jose/Rio Shutaque WEAP applications. The starting point for this analysis was to define the range of potential climatic conditions in 2050 in the two systems using output from the Hadley (Had) and Generalized Fluid Dynamics Laboratory (GFDL) models. Output from the GFDL model run under the B2 emissions scenario was used, while output for the A2, B2, and A1fi emissions scenarios was extracted from the Had model.

Notice that while all GCM/emission scenario combinations predict that temperatures will increase in Guatemala in 2050, the GFDL model suggests that precipitation will increase relative to historical conditions in 2050 while the Had model predicts drier conditions. Using these the climate time series derived from consideration of the GCM output to run the Rio Naranjo and Rio San Jose/Rio Shutaque WEAP applications, it was possible to assess what the impact would be on critical water factors.

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Key findings from Guatemala NCAP Project

Lessons learned from Guatemala NCAP Project