Estimation of Evaporation Losses in Arid Areas: A Case Study of Kailana and Takhatsagar, Jodhpur, Rajasthan, India

Abstract

Kailana and Takhatsagar reservoirs are two key water bodies in Jodhpur, Rajasthan (India), serving as the principal raw water storage sources for the city’s water supply. This study quantifies evaporation losses from these reservoirs and evaluates their implications for water management in an arid environment. Kailana and Takhatsagar have storage capacities of 4.81 Mm³ and 6.52 Mm³, respectively. Their primary source of inflow is the Rajeev Gandhi Lift Canal (RGLC), supplemented by limited runoff from surrounding hills during rainfall events. An evaporation estimation model was developed using relevant meteorological parameters to assess daily evaporation losses. Because evaporation is strongly influenced by the exposed water surface area, depth–area relationships were also established for both reservoirs to improve estimation accuracy. The results indicate pronounced seasonal variability in evaporation, ranging from a minimum of 2.73 mm day⁻¹ in winter to a maximum of 13.76 mm day⁻¹ during summer. At full supply level, the combined average evaporation loss from both reservoirs is approximately 9,733.6 m³ day⁻¹. Recent studies suggest that evaporation from Indian reservoirs has increased by about 5.9% per decade between 1985 and 2018 due to climate change and expanding reservoir surface areas, intensifying water stress in arid regions such as Rajasthan. The model developed in this study provides a practical tool for incorporating evaporation losses into reservoir water budgeting and for supporting long-term water resource planning.