Trends in 20 extreme indices of temperature and precipitation are examined for Sri Lanka using high-quality datasets for 19 meteorological stations, for a period between 1980 and 2015. It is evident that annually averaged mean minimum temperatures are increasing across most of Sri Lanka. The difference between maximum and minimum temperatures, diurnal temperature range is decreasing, indicating that the minimum temperature is increasing faster than the maximum temperature. Significant decrease in the annual occurrence of cold nights and increase in the annual occurrence of warm nights are also obvious. When compared with temperature changes, less spatially coherent pattern of change and a lower level of statistical significance were observed in precipitation indices. The annual total precipitation (PRCPTOT) has indicated a significant increasing over 1980-2015. More than 80% of stations showed an increasing trend in precipitation indices. The trends in extreme precipitation events such as maximum one-day precipitation, maximum five-day precipitation, and total precipitation on extreme rainfall days (R95p and R99p) are increasing at most locations, indicating that the intensity of the rainfall is increasing. Increase of precipitation extreme trends indicates that occurrence of extreme rainfall events notably influences total annual precipitation in Sri Lanka. Therefore, the observed increases in total rainfall observed in many locations may be due in part to an increase in of extreme rainfall events. Patterns of change in precipitation extremes are more heavily influencing the climate variability by aggravating the variability, significantly influencing climate sensitive sectors such as agriculture and water resource management.

The anomalous circulation patterns during an unusually prolonged stormy-weather period in Hawaii from 19 February to 2 April 2006 are analyzed and are compared with those of two previously known prolonged heavy-rainfall periods (March 1951 andFebruary 1979). The circulation patterns for these three periods are characterized by 1) a negative Pacific-North American (PNA) pattern in the midlatitudes with a blocking high southwest of the Aleutian Islands, 2) retraction and splitting of the zonal jet into a polar jet north of 508N and a persistent subtropical jet to the south over the central Pacific Ocean, 3) an anomalous low west of the Hawaiian Islands embedded in the subtropical jet, and 4) a weaker-than-normal Hadley circulation in the mid-Pacific. The moisture advected from low latitudes by the southerly wind component east of the persistent anomalous low, combined with upward motion, provides the large-scale setting for the unusually prolonged unsettled weather across the Hawaiian Islands. For all three cases, the prolonged stormy weather started after the onset of large-scale blocking and a negative PNA pattern over the North Pacific and the occurrence of a persistent anomalous low embedded in the subtropical jet west of the Hawaiian Islands. Furthermore, the persistent low was located at the optimal position to bring moisture from the central equatorial Pacific to Hawaii. The stormy weather ceased after the midlatitude blocking pattern weakened and the anomalous low in the subtropics decayed and/or shifted westward. There are no apparent common precursors in the 2-week period prior to the prolonged stormy weather among these three cases, however. FIG. 4. (a) Mean moisture flux yq (contour interval every 10 g kg 21 m s 21 ) at the 850-hPa level and (b) mean transient moisture flux y9q9 (contour interval every 1 g kg 21 m s 21 ) at the 850-hPa level during

The aim of this study was to assess the application of gridded precipitation datasets for applications in Sri Lanka and to identify suitable products that can be used for hydrological applications in data sparse regions. Here, nine global datasets were considered for this study, and after initial screening, four datasets, such as Integrated Multi-Satellite Retrievals for GPM (IMERG) early run calibrated, Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS), European Center for Medium range Weather Forecasting (ECMWF)-ReAnalysis (ERA5) and Indian Monsoon Data Assimilation and Reanalysis (IMDAA), were selected for detailed comparison. These data products were analysed at monthly, seasonal and annual time scale for whole Sri Lanka and also for three distinguished climate zones (wet, intermediate and dry) for the period 2001-2015. The datasets were further evaluated based on their ability to capture the extreme events, based on recent designated dry year and wet year. All four datasets represent the annual and monthly climatology of Sri Lanka well; however, discrepancies are seen at seasonal scale.CHIRPS had the best performance in the wet zone and ERA5 in dry and intermediate zones. Although all datasets distinctly identified the wet year and dry year with respect to the normal average, the interannual variability was explicitly identified by CHIRPS and ERA5. Therefore, for replicating the national and zonal climatology, both ERA5 (dry and intermediate zones) and CHIRPS (wet zone) are suitable. With the perspective of hydrological applications, both datasets can be used in development of hydrological models for applications such as flood forecasting, reservoir management and climate change impact assessment as an alternative to observed rainfall data in data scarce regions.

No abstract