SWAT: Custom Weather Generator Tips

This blog contains

• RAINHHMX & RAIN_YRS estimation/assumption for creating User Weather Generator
• Global Weather Data: Positive Bias in Precipitation Data

a. RAINHHMX and RAIN_YRS

SWAT users may need to create their own Weather Generator for their own project. However, maximum 0.5 hour rainfall information is usually unavailable. In my project, I addressed this problem by following Dr. Srinivasan's suggestion:

RAINHHMX of a given month = (Maximum Daily Precipitation recorded in given month)/3

Furthermore, I used RAIN_YRS = 10 in my User Weather Generator.

b. Global Weather Data

Worldwide weather data is made available to SWAT users via Global Weather Data. 

I downloaded data from Global Weather Data (GWD) for my project, which is on a lake watershed in northwestern Turkey (Fig. 1). When I compared GWD precipitation with the measured precipitation (obtained from Turkish Meteorological Service (MGM)), I noticed that GWD precipitation was substantially higher than the measured one, especially for the wet months (Fig. 2).   

Therefore, I highly recommend cautious use of GWD precipitation data due to the fact that this data can have very significant positive bias. 

 

Figure 1. Location of my study area and weather stations.

Distance between MGM Stations & GWD Stations:

- Bolu - 407319: 23 km

- Gerede - 407322: 7 km

Figure 2. Average monthly precipitation of the weather stations.

Mean Annual Precipitation Comparison:

• Bolu: 554.7 mm              407319: 1293.8 mm
• Gerede: 677.0 mm          407322: 1163.5 mm