WFM 6202: Remote Sensing and GIS in Water Management [Part-B: Geographic Information System (GIS)] Case study: Generation of rainfall contour map using spatial analysis of GIS Akm Saiful Islam Institute of Water and Flood Management (IWFM) Bangladesh University of Engineering and Technology (BUET) February, 2008

Problem statement “This case study will show how to generate a rainfall contour map of over Bangladesh based on the data collected in different rain gauge stations.” Given data: A shape file which contains different Thana boundary of Bangladesh A text file contains locations of rain gauge stations and mean daily rainfall values (mm/day) of that station

Outline of the Exercise Create a Shape file of rain gauges from station data in a ASCII text file Creating District map of Bangladesh using generalization technique from Thana map of Bangladesh. Create rainfall contour map of rainfall of Bangladesh by surface interpolation

Add Thana Shape file of Bangladesh

Create District Maps from Thana Maps Click on Dissolve tools Select District name field

District Maps of Bangladesh with unique color

Change Layer Property Double click on the Layer Select Categories from Symbology tab District name as Value Field Click on Add All values You can also change color scheme

District Map of Bangladesh Rename the layer as District

Add Rainfall Text files as table Click on Add Data and select rainfall.txt Open it as table

Table of Rainfall Data

Create Shape file from Rainfall table Click on Make XY Event Layer Select rainfall table Longitude as X Field and Latitude as Y field

Rain gauge stations as shape file

Rain gauge stations Label features

Turn on Spatial Analyst Extension First load the Spatial Analyst click on Tools > Extension Check the box left to Spatial Analyst

Masks Interpolation region Click options from Spatial Analyst Select District as analysis mask

Step-7: Create contour of rainfall by surface interpolation Click Surface > Interpolate Grid Select Output grid extent as Disolv1.shp Select MeanDailyRain as Z Value Field

Interpolation using IDW method Click on IDW method of interpolation Select Z value field as MeanDailyRain

Rainfall map of Bangladesh

Find Mean Rainfall for each district Click Zonal Statistics

Zonal statistics for each distric

Rainfall in each district of Bangladesh Change symbology of district maps to zstat.MEAN Turn on Label