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Nepal Hazard Risk Assessment 3 ANNEXURE 3 DROUGHT HAZARD ASSESSMENT METHODOLOGY (a) Moderate drought in Winter (b) Severe drought in Winter In order to understand the drought hazard in Nepal, the SPI was used to quantify the precipitation deficit for multiple time scales, which reflect the impact of drought in different locations of Nepal. It is reasonable and more convenient to assess drought hazard and analysis at least by using two indices viz: 1. Standardized Precipitation Index (SPI) 2. The Soil Moisture Index (SMI) % of stations 50 40 30 20 10 0 1978 1981 1984 1987 1990 1993 1996 1999 2002 2005 % of stations 50 40 30 20 10 0 1978 1981 1984 1987 1990 1993 1996 1999 2002 2005 3.1 STANDARDIZED PRECIPITATION INDEX (SPI) Year Year SPI has been computed for all the seasons from 1977 to 2007 to investigate the spatial and temporal variation of drought and its severity. (c) Extreme drought in Winter (a) Temporal variation of drought Year to year variation of SPI for winter, premonsoon, monsoon and postmonsoon seasons for each station were computed. In order to comprehend the behavior of drought more concisely and holistically interannual variation of moderate to extreme drought occurrence (expressed in percentage of “drought” station out of all data available stations) was also computed (Figure 3.1 - Figure 3.4). The figures show that drought of all category occurs in Nepal in all seasons. It seems that moderate drought frequently occurs in all the seasons. But severe and extreme droughts in comparison are less common. All categories of drought show increasing trend in winter season. Severe and extreme droughts which used to be less common in winter season have now been observed in many stations recently. It indicates that winter droughts are getting intense in Nepal. During the premonsoon season, moderate drought show slightly increasing trend but the severe and extreme drought both showed decreasing trend. This means less number of stations recorded intense droughts in the recent decade during the premonsoon season. In the monsoon season the trend in all categories of drought are decreasing. Interestingly, the extreme droughts have occurred sporadically during monsoon however, there was a lull period in the 90's. On the contrary, during the 90's the severe drought was experienced in more stations in the postmonsoon season. Extreme droughts though occurred during the 80's and 90's in this season but were observed only in few places. From 2001 to 2007 the extreme drought was not recorded at all. (a) % of stations 35 30 25 20 15 10 5 0 % of stations 50 40 30 20 10 0 1978 1981 1984 1987 1990 1993 1996 1999 2002 2005 Year Figure 3.1. Interannual variation of a) moderate b) severe and c) extreme drought occurrence during winter Moderate drought in Premonsoon (b) Severe drought in Premonsoon 35 30 % of stations 25 20 15 10 5 0 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004 2007 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004 2007 Year Year 106
Nepal Hazard Risk Assessment (c) % of stations 35 30 25 20 15 10 5 0 1977 Extreme drought in Premonsoon 1980 1983 1986 1989 1992 1995 1998 2001 Year 2004 2007 (a) Moderate drought in Postmonsoon 50 % of stations 40 30 20 10 0 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004 Year 2007 (b) % of stations 50 40 30 20 10 0 1977 Severe drought in Postmonsoon 1980 1983 1986 1989 1992 1995 1998 2001 Year 2004 2007 Figure 3.2. Interannual variation of a) moderate b) severe and c) extreme drought occurrence during premonsoon (c) Extreme drought in Postmonsoon (a) % of stations 40 30 20 10 0 1977 Moderate drought in Monsoon 1980 1983 1986 1989 1992 1995 1998 2001 Year 2004 2007 (b) % of stations 40 30 20 10 0 1977 Severe drought in Monsoon 1980 1983 1986 1989 1992 1995 1998 2001 Year 2004 2007 % of stations 50 40 30 20 10 0 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004 2007 Year Figure 3.4. Interannual variation of a) moderate b) severe and c) extreme drought occurrence during postmonsoon (c) % of stations 40 30 20 10 Extreme drought in Monsoon The result coming out from these graphs (Figure 3.1 - Figure 3.4) is as shown in Table 3.1. Table 3.1: Summary of drought situation Drought type Winter Premonsoon Monsoon Postmonsoon 0 1977 1980 1983 1986 1989 1992 Year 1995 1998 2001 2004 Moderate Most common Occur most frequently Most common Sporadic but reported in less number of stations recently Figure 3.3. Interannual variation of a) moderate b) severe and c) extreme drought occurrence during monsoon Severe Sporadic but reported in more stations recently Less occurrence in recent years. 1996 a worst premonsoon drought year Occur intermittently Infrequent. Common during 1988 to 1994. 107
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