arid environments evapotranspiration is influenced directly by the amount of precipitation because arid regions have low humidity and low precipitation. Our study area, with a semi-arid climate, shows that the rate of evapotranspiration generally follows the precipitation trend (Fig. 5). However, other factors, such as wind speed, solar radiation, albedo, and humidity, must also be considered to understand the evapotranspiration response rate clearly.
6. CONCLUSIONS
This study investigated the climate and land-cover changes impact on water resources in a semi-arid watershed from 1970 - 2009. We selected a semi-arid watershed where human impact is minimal to understand the natural response of water resources to climate and land-cover changes. SWAT simulations were conducted to evaluate the water resource component employing three different land cover data sets representing three different sub-periods: 1970s/1980s, 1990s, and 2000s. The study area experienced a 0.9°C increase in temperature and a 10.9% decrease in precipitation during the forty recorded years. Compared to previous studies on semi-arid climates the study area had a lower rate of temperature increase and a similar decreasing trend in precipitation. We found that an increase in temperature in the study area was not as significant if the human development factor was removed. Precipitation generally follows a decreasing pattern as with other semi-arid locations. The two predominant land-cover change trends were the conversion of grass and forest lands into bush/shrub lands and developed and crop lands conversion into barren and grass lands. These changes indicate that conversions into barren and grass lands were influenced by a decrease in human activity. It is further suggested that changes in temperature and precipitation affected land-cover changes including the types of vegetation where human intervention is minimal. We noted a 10.2% decrease in surface runoff, a 10.0% decrease in groundwater discharge, a 4.1% decrease in soil water content, and a 10.5% decrease in evapotranspiration. In the study area surface runoff, groundwater discharge and evapotranspiration generally followed similar trends to that of precipitation when human impact is minimal. The soil water content is relatively sensitive to land-cover change where a decrease in precipitation is offset by the impact of land-cover changes.
Acknowledgements This work was supported by the National Research Foundation of Korea Grant funded by the Korean Government (NRF-2012R1A1A1041589).