3.1 Temperature and precipitation trend:
The temperature and precipitation trend of Butwal from the year 1987–2017 was analyzed and found that the year 2017 received maximum total annual rainfall with 3525.5 mm and maximum average annual rainfall 293.8 mm and also 2017 receive the highest average monsoon rainfall (818.9 mm), followed by 2016, with total annual rainfall and highest average monsoon rainfall of 3368.1 mm and 766.4 mm respectively (figure 3). Total minimum annual rainfall was recorded in 2012 with 1223.9 mm and minimum average annual rainfall 101.99 mm (figure 2 a) and 2012 also received the lowest average monsoon rainfall of 284.6 mm, followed by 2005 (286.1 mm) (figure 3). Likewise, high maximum temperatures were recorded in the years 1992, 2010, and 2016 with 39.8, 39.6, and 39.6 °C respectively whereas 2016, 2011, 2017 have the highest average annual maximum temperature with 31.7, 31.69, and 31.65 °C (figure 2 b). And, the lowest minimum temperature was recorded in 2006 and 2012 with 8.8 °C each, followed by 1998 and 2017 with 9.2 °C each but the average annual minimum temperature were minimum on the year of 2011, 1987, and 2012 with 16.74, 17.83, and 18.73°C (figure 2 c). Similarly, the year 2009 received the highest average temperature of 26.39°C, followed by 2006 and 2005, with 26.35 and 26.23°C and the year 2011 received a minimum average temperature of 24.21 °C, followed by 1987 and 2013 with 24.25 and 24.34 °C (figure 2 d).
3.2 Drought occurrence, frequency, and intensity:
Butwal suffered from extreme meteorological drought in January 1998, July 2005, October 2011, and January 2012 respectively. Similarly, the city also suffered from extreme agricultural drought in July 2005 and June 2012. Likewise, in August 2012 and January to February 2013, the city suffered from extreme hydrological drought.
The city suffered from the longest severe hydrological drought from August 2012 to May 2014, followed by from October 2000 to August 2001. Similarly, a severe hydrological drought occurred for three, four, and six consecutive months in 1999, 2013, and 2010 respectively. The year 1998 received severe agricultural drought for four consecutive months and 2012 received severe agricultural drought for seven months.
Looking at the drought’s intensity and duration, the drought of 2012 can be considered as the most intensive drought as Butwal suffered from severe and extreme meteorological, agricultural and hydrological drought in 2012. Besides, the year also suffered from drought in summer as well as in winter.
Table 3: Drought frequency
Various month SPEI
|
Drought characteristics
|
Frequency
|
SPEI 1
|
Moderate drought
|
10.8
|
Severe drought
|
3.8
|
Extreme drought
|
1.1
|
SPEI 3
|
Moderate drought
|
13.2
|
Severe drought
|
4.3
|
Extreme drought
|
0.5
|
SPEI 6
|
Moderate drought
|
12.4
|
Severe drought
|
5.1
|
Extreme drought
|
0.3
|
SPEI 12
|
Moderate drought
|
15.6
|
Severe drought
|
4.0
|
Extreme drought
|
0.3
|
SPEI 18
|
Moderate drought
|
12.4
|
Severe drought
|
4.0
|
Extreme drought
|
0.5
|
SPEI 24
|
Moderate drought
|
7.3
|
Severe drought
|
7.0
|
Extreme drought
|
0.0
|
Table 3 shows the relationship between drought intensity and frequency. The data collected from FGDs and KIIs have elucidated drought occurrence and intensity status in our study area. The survey result supported that the Tinau river, which was perennial about three decades ago has recently started drying up during summer. Local farmers have also stated that the irrigation canals which was used to irrigate the agricultural lands around Butwal have recently started drying up between the mid of March to the mid of July. They also added that the groundwater level has significantly decreased as they are experiencing the need to burying pipes deeper than before to extract the groundwater.
3.3 Drought vulnerable map:
Figure 5 shows that the central and the southern part of the city is more vulnerable to drought in comparison to the northern part. While looking at each vulnerable class, it was found that most of the city’s area (41.12 km2) was low vulnerable to drought followed by 38.47 km2 of highly vulnerable area, 16.69 km2 of moderately vulnerable area, 5.24 km2 of very highly vulnerable area, and 0.08 km2 of very low vulnerable area (Table 4).
Table 4: Drought vulnerable class with corresponding areas.
NDDI Value
|
Vulnerable Class
|
Area (km2)
|
Percentage (%)
|
<-2
|
Very low vulnerable
|
0.08
|
0.08
|
-2–0.7
|
Low vulnerable
|
41.12
|
40.44
|
0.7–1.25
|
Moderately vulnerable
|
16.69
|
16.41
|
1.25–3
|
Highly vulnerable
|
38.47
|
37.83
|
>3
|
Very highly vulnerable
|
5.53
|
5.24
|
|
Total
|
101.69
|
100
|
3.4 Flood years on Butwal:
From KII and FGD, it was found that floods occurred in Butwal in 1968, 1970, 1971, 1974, 1979, 1981, 1991, 1993, (1996–1998), 2005, 2007, 2008, 2009, 2011, 2013 and from (2014–2017) with significant loss of lives, properties, and infrastructures. It was also found that the Tinaus’ Bifurcation was caused by the flood of 1981.
According to key informants, major floods occurred in Butwal, in 1970, 1981, 2005, and 2017. A possible reason provided by key informants during KII and FGD was the deepening of the river due to the over-extraction of river bed materials.
3.5 Flood Vulnerability Mapping:
Vulnerability for each variable responsible for flood occurrence was identified through the reclassification and mapping of these variables was done. A1 in figure 6 indicates the status of the elevation variable and A2 indicates the vulnerability of elevation for a flood. Similarly, the status of the slope, precipitation, proximity to the river, land cover, and soil types visualized through B1, C1, D1, E1, F1, and their respective vulnerability for flood were indicated by B2, C2, D2, E2, F2 (Figure 6). The Natural Break method was used to reclassify the elevation, slope, and precipitation. The elevation range was from 56m to 1047m (A1) where most of the land was under the low elevation range (A2 in Figure 6). The range for the slope was 0 to 59.18 degrees (B1) and the northern part was found less vulnerable due to the high slope compared to the central and southern part of Butwal (B2 in Figure 6). Precipitation was found higher on the eastern and central part of Butwal (C1), so was more vulnerable to flooding (C2 in Figure 6). The river passed through the northern part where it bifurcated in the center, one towards the southeastern and another on the southwestern part (D1). The land close to the river was more vulnerable than others (D2 in Figure 6). Four landcover types i.e. forest, agricultural land, settlement, and river were classified with an overall accuracy of 90.3% and kappa statistic 0.84 (confusion matrix in Appendix 1). Forest was found on the higher elevation and slope, agricultural land and settlement were near to river (E1). Thus, the river, agricultural land, and settlement were more vulnerable to flood than forest (E2 in Figure 6). Four types of soil i.e. eutric fluvisols, eutric gleysols, calcaric phaeozems, and dystric regosols were identified (F1) where and eutric fluvisols and eutric gleysols were more sensitive to flood, due to their low infiltration rate and being near to the river. Area with dystric regosols was found less vulnerable to flood because of its higher infiltration rate and geographical location (higher elevation and sloppy areas) (F2 in Figure 6).
The central and southern part of the Butwal was found more vulnerable to flood, with 26.32 km2 followed by 27.86 km2 and 13.956 km2 as extremely high vulnerable, highly vulnerable, and vulnerable, in comparison to the northern part from the visual interpretation of the Flood Vulnerability Map (Figure 7).
About 68% of the land was found vulnerable to flood and more specifically 26.47% of the land was extremely high vulnerable followed by 28% and 14.03% as highly vulnerable and vulnerable respectively. About 31.94% of the land was found less vulnerable with 18.96% moderately vulnerable and 12.53% least vulnerable (Table 5).
Table 5: Flood vulnerable class with corresponding areas
Reclassified Value
|
Vulnerable Class
|
Area (km2)
|
Percentage (%)
|
1
|
Extremely High Vulnerable
|
26.92
|
26.47
|
2
|
High Vulnerable
|
28.47
|
28
|
3
|
Vulnerable
|
14.27
|
14.03
|
4
|
Moderately Vulnerable
|
19.28
|
18.96
|
5
|
Least vulnerable
|
12.74
|
12.53
|
|
Total
|
101.69
|
100
|