Spatial and Temporal Variations in Rainfall and the ENSO-rainfall Relationship over Sarawak, Malaysian Borneo

To determine the spatial and temporal variations in the El Nino Southern Oscillation (ENSO)-rainfall relationship and seasonal variation in rainfall over northern Borneo, simultaneous and lag correlations between the December-February (DJF) average Nino-3.4 (5°S-5°N, 170°-120°W) sea surface temperature (SST) and rainfall were examined using rainfall data from 18 stations throughout Sarawak during 1963-2003. The lag correlations for June-August (JJA) rainfall and SST were significantly negative over southwestern Sarawak (SWS), but the simultaneous correlations for DJF rainfall and SST were significantly negative over northeastern Sarawak (NES). We categorized the 18 stations into four clusters (C1-C4) according to the variation of the seasonal fluctuation in rainfall. C1 and C2 are located in SWS along the convex and concave coastline, respectively, whereas C3 and C4 are located in NES along the convex and straight coastline, respectively. C2 and C4 are also located in the interior in SWS and NES respectively. From the composite of monthly rainfall for all clusters, a decrease in rainfall in JJA was found for all regions in El Nino years but only for C2, C3 and C4 in DJF during the warm phase of ENSO. The C3 region may be the most vulnerable to El Nino-induced droughts in Sarawak.