Spatial and Temporal Analysis of Extreme Precipitation under Climate Change over Gandaki Province, Nepal

Abstract

This paper presents a research study of expected precipitation extremes across the Gandaki Province, Nepal. The study used five indices to assess extreme precipitation under climate change. Precipitation output of two Global Climate Models (GCMs) of Coupled Model Intercomparison Project Phase Six (CMIP6) were used to characterize the future precipitation extremes during the rainfall season from June to September (JJAS) and overall days of the year. To characterize extreme precipitation events, we used daily precipitation under the SSP2–4.5 and SSP5–8.5 scenarios from the Beijing Climate Center and China Meteorological Administration, China; and Meteorological Research Institute (MRI), Japan. Considering large uncertainties with GCM outputs and different downscaling (including bias correction) methods, direct use of GCM outputs were made to find change in precipitation pattern for future climate. For 5-, 10-, 20-, 50-, and 100-year return periods, observed and projected 24 h and 72 h annual maximum time series were used to calculate the return level. The result showed an increase in simple daily intensity index (SDII) in the near future (2021–2040) and far future (2081–2100), with respect to the base-year (1995–2014). Similarly, heavy precipitation days (R50 mm), very heavy precipitation days (R100 mm), annual daily maximum precipitation (RX1day), and annual three-day maximum precipitation (RX3day) indices demonstrated an increase in extreme precipitation toward the end of the 21st century. A comparison of R50 mm and R100 mm values showed an extensive (22.6% and 63.8%) increase in extreme precipitation days in the near future and far future. Excessive precipitation was forecasted over Kaski, Nawalparasi East, Syangja, and the western half of the Tanahun region. The expected increase in extreme precipitation may pose a severe threat to the long-term viability of social infrastructure, as well as environmental health. The findings of these studies will provide an opportunity to better understand the origins of severe events and the ability of CMIP6 model outputs to estimate anticipated changes. More research into the underlying physical factors that modulate the occurrence of extreme incidences expected for relevant policies is suggested.

Return Periods in Assessing Climate Change Risks: Uses and Misuses

“…According to them, when an event is given a high or virtually certain likelihood, it must have a high confidence and never low confidence, or else it is not possible to be interpreted in a meaningful way. By assigning metrics on a scale [1,10] (Table 3), probabilities absorb degrees of confidence, increasing their accuracy. Even if it is considered that sea level has exceeded present levels during the last 2000-5000 years, approximately (Figure 2b), the fact that the previous interval occurrence lasted more than 120,000 years means that the average return period will be very high and the probability of occurrence will remain close to zero.…”

“…According to them, when an event is given a high or virtually certain likelihood, it must have a high confidence and never low confidence, or else it is not possible to be interpreted in a meaningful way. By assigning metrics on a scale [1,10] (Table 3), probabilities absorb degrees of confidence, increasing their accuracy. So, when IPCC reports say that SLR in Japan is "likely" to occur with "medium confidence", the proposed probability scale level is assigned as "7", while, in the case of extreme precipitation that is "extremely likely" to occur with "very high confidence", the probability scale is equal to "10".…”

“…Return periods have been widely used to assess the probability of occurrence of most natural hazards, such as earthquakes [4], tsunamis [5], extreme heat/cold weather occurrences [6][7][8], extreme precipitation [9,10], storm surges [11], tropical/extratropical cyclones [12], landslides [13].…”

Climate change research, capacity building and communication on climate extremes over South Asia

“…Nepal has experienced extreme events due to climate extremes in recent decades. Studies claimed that heavy and extreme rainfall will increase under the RCP4.5 and RCP8.5 over Nepal (Chapagain et al, 2021;Pandey & Mishra, 2022). Hence, the importance of research in elucidating the changing patterns and impacts of climate extremes in South Asia cannot be overstated.…”