Rainfall Analysis and Comparison of Water Balance of Meteorological Stations in the Mountain Desert and Wet Zone in Gandaki Basin

Abstract

Water is essential to every human community and is essential resource for economic development, agriculture, productivity, industrial growth etc. Of all the resources of water the primary source of water is rain. The rain water will recharge the ground water and the remaining water will transformed as surface flow. In the study the water budget in the two considered stations are found to be entirely different. Lumle on the windward side of the Annapurna Range is dominated by Monsoonal rainfall and therefore have surplus of water. Scarcity of water is observed in the winter season. While as in the case of Jomsom there is deficit of water with in whole year. Only in the month of February there seems to be water. In contrast in the case of Jomsom lie on the leeward side of the Annapurna range, experienced deficit of water during whole year. However, in February there is a slight surplus of water mainly due to western disturbances.

Lumle receives the highest annual rainfall in Nepal which amounts 5430mm of rainfall. During monsoon season (June-September) it receives about 4595mm amounting about 84.63% of the annual value while in the pre-monsoon season (March-May) , post-monsoon season (October-November) and winter season (December-February) it receives about 487mm(9%), 247mm(4.55%)and 100mm(1.85%) respectively. Jomsom on the other hand receives about 263mm of annual rainfall out of which about 138mm (about11.5%) during monsoon season, 58.88mm (22.37%) during pre-monsoon season, 36.48mm (13.86%) in post monsoon season and 30.37mm (11.54%) in the winter season. There conclusions made from the study of the water availability and surplus of water in the Kali Gandaki watershed basin are: Potential evapotranspiration is the function of temperature and the geological texture and the high mountain range therefore the water surplus is more in the southern belt of the basin and exceeds the maximum in Lumle, as Lumle receives the maximum annual rainfall throughout the country while decreases drastically towards the north though the distance between the station are not so far the decreasing precipitation is because of high Annapurna Himalayan region. The study shows the orographic effects on precipitation within the south- facing slopes of the Himalayas. This region showed extremely large gradients in rainfall over small spatial scales (10–20 km), on the timescales of both the monsoon season as well as individual weather events. From the isohyetal map analysis for the average annual rainfall and during for the monsoon and post monsoon, the maximum gradient is at Lumle while as the minimum gradient is towards Jomsom and some secondary high pockets of rainfall are found to be at Baghara as well as Muna. For pre monsoon highest pocket is found to be at Lumle and lower towards north of Jomsom. But for the winter, the high pockets are seen vicinity of Lumle and Beni Bazaar and secondary high pocket at Jomsom but lower toward northern part.