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This paper describes the establishment of a dense rain gauge network andsmall-scale variability in rain events (both in space and time) over acomplex hilly terrain in Southeast India. Three years of high-resolutiongauge measurements are used to validate 3-hourly rainfall and sub-dailyvariations of four widely used multi-satellite precipitation estimates(MPEs). The network, established as part of the Megha-Tropiques validationprogram, consists of 36 rain gauges arranged in a near-square grid area of50 km  ×  50 km with an intergauge distance of 6–12 km.Morphological features of rainfall in two principal rainy seasons (southwestmonsoon, SWM, and northeast monsoon, NEM) show marked differences. The NEMrainfall exhibits significant spatial variability and most of the rainfall isassociated with large-scale/long-lived systems (during wet spells), whereasthe contribution from small-scale/short-lived systems is considerable duringthe SWM. Rain events with longer duration and copious rainfall are seenmostly in the western quadrants (a quadrant is 1/4 of the study region) inthe SWM and northern quadrants in the NEM, indicating complex spatialvariability within the study region. The diurnal cycle also exhibits largespatial and seasonal variability with larger diurnal amplitudes at all thegauge locations (except for 1) during the SWM and smaller and insignificantdiurnal amplitudes at many gauge locations during the NEM. On average, thediurnal amplitudes are a factor of 2 larger in the SWM than in the NEM. The24 h harmonic explains about 70 % of total variance in the SWM and only∼ 30 % in the NEM. During the SWM, the rainfall peak is observedbetween 20:00 and 02:00 IST (Indian Standard Time) and is attributed to thepropagating systems from the west coast during active monsoon spells.Correlograms with different temporal integrations of rainfall data (1, 3, 12,24 h) show an increase in the spatial correlation with temporal integration,but the correlation remains nearly the same after 12 h of integration inboth monsoon seasons. The 1 h resolution data show the steepest reduction incorrelation with intergauge distance and the correlation becomesinsignificant after ∼ 30 km in both monsoon seasons.  Validation of high-resolution rainfall estimates from various MPEs againstthe gauge rainfall data indicates that all MPEs underestimate the light andheavy rain. The MPEs exhibit good detection skills of rain at both 3 and24 h resolutions; however, considerable improvement is observed at 24 hresolution. Among the different MPEs investigated, the Climate PredictionCentre morphing technique (CMORPH) performs better at 3-hourly resolution inboth monsoons. The performance of Tropical Rainfall Measuring Mission (TRMM)multi-satellite precipitation analysis (TMPA) is much better at dailyresolution than at 3-hourly, as evidenced by better statistical metrics thanthe other MPEs. All MPEs captured the basic shape of the diurnal cycle andthe amplitude quite well, but failed to reproduce the weak/insignificantdiurnal cycle in the NEM

hydrology and earth system sciences

Assessment of small-scale variability of rainfall and multi-satellite precipitation estimates using measurements from a dense rain gauge network in Southeast India