Nepal Hazard Risk Assessment - Asia-Pacific Gateway for Disaster ...

Nepal Hazard Risk Assessment
3.5 DROUGHT HAZARD ASSESSMENT
3.5.1 MAP CONTENT
The map shows set of drought susceptibility maps developed based on Standard Precipitation Index
(SPI). The SPI has been developed on the data collected from uniformly distributed 40 meteorological
stations across the country for the time span of more than three decades. The susceptibility maps have
been developed based on the probability of occurrence of droughts with class of severity such as
moderate, severe, extreme and moderate to extreme. The map shows the variation of drought in various
seasons i.e. winter, Pre monsoon, Monsoon and Post Monsoon.
3.5.2 APPLICATION OF MAPS WITH RESPECT TO DISASTER RISK MANAGEMENT
The maps will form the basis for understanding the drought prone areas and temporal variation of
drought in various regions. Various focal sectors like agriculture, water resources, disaster management
and Irrigation may use the maps for water and food security in the region, development of national and
regional plan for sustained agricultural development, Assess the climate change impact and develop the
strategy for redefining the cropping pattern and water conservation. The maps will help central and local
government to take proactive measures for allocation of resources and relief management.
3.5.3 DATA AVAILABILITY FROM SOURCES
Reliable supporting documents, maps, appropriate models and methods for drought assessment were
collected from different sources. Based on data quality, quantity and their spatial distribution overall 40
stations were selected as representative stations covering the entire country. The necessary climatic data
required for computing the indices, i.e., monthly total rainfall and monthly mean temperature were
collected from Department of Hydrology and Meteorology for the period of 1977-2007. Some of the
sources for data is as below:
• Central Bureau Statistics (CBS), 2005. Statistical Year book, Nepal.
• DHM, 2001. Weekly Dry Spell Atlas of Nepal: Final Report.
• DHM, 2001-2009. Preliminary monthly weather summary of Nepal from 2001 to 2008, Department
of Hydrology and Meteorology.
• DHM, 2009. Dry and Warm Winter 2009, Climate Section, Internal report of Department of
Hydrology and Meteorology.
• Gibbs, W. J. and Maher, J. V., 1967. Rainfall deciles as drought indicators. Bureau of Meteorology
Bulletin, No. 48, Commonwealth of Australia, Melbourne.
• National Climatic Data Center, 2006. Climate of 2006, U.S. Standardized Precipitation Index.
• NDMC, 2009. Monitoring Drought. National Drought Mitigation Centre, University of Nebraska–Lincoln
• Thornthwaite, C. W., 1948: An approach toward a rational classification of climate. Geographical
Review, 38, 55–94.
• World Meteorological Organization, 2005. Meteoworld (weather. Climate. Water), WMO , August
2005.
• World Meteorological Organization, 1992. International Meteorological Vocabulary, WMO Report
NO. 182, 2nd and. WMO: Geneva; 784.
3.5.4 SPECIAL REMARK
• The drought assessment has been carried out using two most practiced Indices namely Standard
Precipitation Index (SPI) and Soil Moisture Index (SMI). The indices have been developed based on
rainfall collected from uniformly distributed meteorological stations and temperature data.
• The drought assessment results from both indices are having similar outcomes. It is observed that
most of the severe to extreme droughts are occurring in winters.
3.5.5 METHODOLOGY
The drought hazard assessment methodology is combined of SPI and SMI. The flowchart in Figure 3.34
shows the process of drought hazard assessment. The SPI has many advantages over other drought
indices, such as the Palmer approach, which requires more variables. The details of the methodology and
outcomes may be referred at Annexure-3.
SPI
Monthly Precipitation Data
Format Data to run the model
(SPI_SL_6.exe)
Monthly and seasonal SPI values
Economy impact
Drought Index: SPI+SMI
Monthly Mean Precipitation
and Temperature Data
SOIL MOISTURE/WATER
SURPLUS/DEFICIENCY
SOIL MOISTURE/WATER
DEFICIENCY
Potential Drought?
Social impact
Compute Heat Index and
Potential evapotranpiration
SMI (I m )= 100(P ‐ PET)/PET
Monthly and seasonal SMI values
Environmental impact
Figure 3.34. Flow chart of drought index computation and its impact in different sectors.
67