| Assessing the Economic Impact of Climate Change – National Case Studies | z
The system’s capacity is under-utilized, which makes it difficult to value the economic damages of climate change and the benefits and costs of avoiding these damages. This is because in practical terms, there is a lot of water available, but not much land that can be irrigated because the infrastructure has been scavenged.
Methods and Data The Methodology for this study consisted of three parts: z
Developing the Base Case,
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Developing the Climate Change Case, and
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Developing the Adaptation/Adjustment Case.
Base Case The purpose of the Base Case analysis was to establish a reference for crop and irrigation water use, crop yields, and net income by both irrigated and non-irrigated (rain-fed) crops in the area. The model was used to calculate the soil water deficit in the area for the various irrigated crops under the climatic conditions of the Base Case. This took into account the effect of temperature on crop water demand. It also took into account the availability of soil moisture carry-over from previous periods as well as inputs of water from precipitation. The amount of irrigation water required to bring each crop to maximum yield was determined through a simple empirical formula – the same for all crops -- developed by Stewart et al. (1977)20 that is a part of CROPWAT. Given the estimated yields and water use, information about average product prices and crop budgets for the area were used to calculate net revenues for each crop. These values were totalled for all crops (twenty-five irrigated and seven non-irrigated) using the observed crop mix in the region. The same approach was used to calculate the yields and net income for crops in the Base Case. However, the crop water requirement for these crops was limited by the amount of precipitation that could effectively reach the root zone of the crops. These detailed data are shown in Annex II, Table II-1.
Climate Change Case The purpose of the climate change case was to show how high, medium and low changes in temperature and precipitation, as projected by Bergant (2006) for 2050 and 2100, would affect crop yields and the net income from irrigated and rain-fed crop production in the region. The detailed temperature and precipitation projections for the climate change cases are shown in Table 5-1. CROPWAT was used to calculate the effects of reduced rainfall and higher temperatures on the soil water balance, crop water demands, and crop yields. Irrigation quantities on irrigated lands were held constant and no additional water was applied to the rain-fed crops in 20
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Stewart, et al. (1977) represents an interesting and straightforward presentation of how CROPWAT can be used in deficit irrigation studies.