Less rain and rainy days—lessons from 45 years of rainfall data (1971–2015) in the Kathmandu Valley, Nepal

Abstract

Understanding spatio-temporal variability in rainfall patterns is crucial for evaluating water balances needed for water resources planning and management. This paper investigates spatio-temporal variability in rainfall and assesses the frequency of daily rainfall observations from seven stations in the Kathmandu Valley, Nepal, from 1971-2015. Daily rainfall totals were classi ed into ve classes, namely, A (light rain, daily rainfall < 10 mm in a day), B (between 10-50 mm), C (between 50-100 mm), D (between 100-150 mm) and E (> 150 mm). The relationship between daily rainfall and rainfall frequency of various rainfall rate classes were analysed. Kriging method was used for interpolation in interpreting seasonal and annual rainfall data and spatial maps were generated using QGIS. The Mann-Kendall (MK) test was performed to determine the temporal trends and Theil-Sen's (TS) slope estimator was used in quantifying the magnitude of trends. Mountain stations showed a decreasing trend in rainfall for all seasons, ranging from − 8.4 mm/year at Sankhu to -21.8 mm/year at Thankot, whereas, a mixed pattern was found on the Valley oor. Mean annual rainfall in the Valley was 1610 mm. Both annual rainfall and the number of rainy days decreased in the Kathmandu Valley over the study period. The study indicated a signi cant reduction in rainfall after 2000. Since springs and shallow groundwater are the primary sources of water supply for residents in the Kathmandu Valley, it is apparent that decreasing rainfall will have (and is already having) an adverse impact on domestic, industrial, and agricultural water supplies, and the livelihoods of people.

Evaluation of gridded precipitation products in the selected sub-basins of Lower Mekong River Basin

“…Saying that, the ranked GPP from this study can be used from different hydro-meteorological application such as water resources planning, estimating potential for hydropower potential, etc. The GPPs are the gateways to fill in the data gaps and spatial coverage for several hydrometeorological studies (Morales-Moraga et al, 2019;Prajapati et al, 2021). However, it should also be noted that the choice of the GPP should be considered based upon the application or purpose of the study as the error in the daily precipitation frequencies and intensities of GPPs significantly impact the output of hydrologic simulations (Luo et al, 2019).…”

Flash Drought Typologies and Societal Impacts: A Worldwide Review of Occurrence, Nomenclature, and Experiences of Local Populations

“…Therefore, Nepal is sensitive to rainfall interruptions in both the main growing season and during winter because rain-fed crops are also grown in this period. Despite annual rainfall totals remaining consistent, the rainfall pattern is becoming more erratic and intense with fewer rainy days and longer dry spells (Prajapati et al 2021). Several terms were identified for dry spells with varying usage around Nepal, including sukkha, or dry condition, ana bristi, referring to scarcity of rain, and khanda bristi, meaning heterogenous summer rain, all of which are known by farmers to reduce crop yield.…”