*2.2. Rain Gauges and Rainfall in Wayanad*

For threshold analyses, the starting point is the collection of rainfall and landslide data [27,35]. Concerning rainfall, despite some recent advances relying on radar measurements, rain gauge is by far the most commonly used method of measurement in threshold analysis [35]. Therefore, rainfall data with the best possible temporal accuracy (daily time steps) were collected from 4 rain gauge stations maintained in the area by the India Meteorological Department (IMD) [46]. The data from 2010 to 2018 are used to carry out the analysis for Wayanad district. The locations of the rain gauge stations are Mananthavady (R1), Vythiri (R2), Ambalavayal (R3) and Kuppadi (R4). The annual cumulative rainfall during the study period is shown in Figure 4. Maximum rainfall was observed in the year of 2018 with a cumulative rainfall of 3832 mm.

**Figure 4.** Annual cumulative rainfall during the study period—district average values.

The decision on choosing the rain gauge or source of rainfall data is an important step in threshold definition. The variation of annual rainfall in four rain gauge stations is depicted in Figure 5. During the study period, R3 and R4 recorded minimum annual rainfalls, and in most of the cases, the annual precipitations recorded at these two gauges were comparable. R1 received a higher amount of rainfall than R3 and R4, while R2 recorded the maximum rainfall in all the 9 years considered. The study can be refined with the availability of rainfall data of better spatial and temporal resolution. The variation in annual rainfall as observed in Figure 5 stresses the difference in meteorological conditions of the four rain gauge areas and the need for separate local scale thresholds.
