Climate Change Impact on Freshwater Resources in a highlands Catchment in Northern Pakistan

Abstract

Pakistan’s water resources are highly vulnerable to climate change threats, so it is expected to affect the water supply-demand balance in this region and challenge existing water management strategies. Population growth is already putting massive pressure on regional water resources, affecting water resources in terms of demand, water-use patterns, and management practices. It is important to have a long and short-term hydrometeorological data to understand the water resources availability and hydrological responses within highlands catchments in northern Pakistan. Hydrometeorological data (temperature, rainfall, inflows, storage, domestic and irrigation releases) of the relevant stations within the study area were analyzed with the aim of detecting trends in seasonal and annual time scales. Considering the importance of climate variability and development in and around the study area on the availability of water, domestic supplies, irrigation demand and other areas of life, trend analysis was applied for two different time periods namely, long-term 1968-2017 and recent development period 1990-2017. The non-parametric Man-Kendall test was used to detect the nature of trends in the hydrological variables. The Sen’s slope estimator and regression analysis were used to determine their significance levels. The study revealed that while the temperature in Rawal catchment is increasing, rainfall is generally decreasing. A significant increase in maximum and minimum temperature is found during the 1968-2017 at 99% and 90% significant level. The rate of increase in the study area is 0.3 °C and 0.106 °C per decade, respectively. However, an insignificant increasing trend is found during 1990-2017. The rate of increase is 0.174 °C and 0.233 °C per decade. A statistically significant increase in average temperature is found during the 1968-2017 at the 99 % level of confidence. The rate of change in the study area is a 19 °C per decade. An insignificant increasing trend in the study area is found during 1990-2017. The rate of change is 0.322 °C per decade. The trend analysis exhibited a non-significant declining trend of rainfall in the study area for the period 1968-2017, the annual rainfall has decreased with a rate of 6.8 mm per decade. A statistically significant trend at the 90% level of confidence is found during 1990-2017. The annual rainfall in the study area has decreased with a rate of 14.33 mm/year. In the study area, about 50% of the average annual rainfall is associated with the summer monsoon. The summer monsoon rainfall in the study area varies from 36 to 65%. A non- xiii significant declining trend of monsoon rainfall is found in the study area during 1968-2017 and 1990-2017. The monsoon rainfall in the study area has no change during 1968-2017 however, decreased with a rate of 79.10 mm/decade during 1990-2017.The significant falling trend in rainfall, especially in the last 30 years, invariably affected water availability and water demand in this region. Seasonal factors unavoidably play a significant role in the availability of water on the river system. This may result in major stresses to the water supply in the near future. The annual inflow and storage of Rawal reservoir records have also been analyzed for the period 1976-2016. Annual rainfall and inflows for the period 1976-2016. The analysis result shows a nearly level insignificant trend in the time series. This analysis of climatic variables at the catchment scale is helpful for the development planning and management of water resources and the development of adaptation strategies in adverse climatic conditions in the region.