Abstract

Long-term variations and trends in a wide range of statistics for daily precipitation characteristics in terms of intensity, frequency and duration in Finland were analysed using precipitation records during 1908–2008 from 3 meteorological stations in the south (Kaisaniemi), centre (Kajaani) and north (Sodankylä). Although precipitation days in northern part were more frequent than in central and southern parts, daily precipitation intensity in the south was generally higher than those in the centre and north of the country. Annual sum of very light precipitation (0 mm < daily precipitation ≤ long-term 50th percentile of daily precipitation more than 0 mm) significantly (p < 0.05) decreased over time, with the highest rate in northern Finland. These decreasing trends might be the result of significant increases in frequency of days with very light precipitation at all the stations, with the highest and lowest rates in northern and southern Finland, respectively. Ratio of annual total precipitation to number of precipitation days also declined in Finland over 1908–2008, with a decreasing north to south gradient. However, annual duration indices of daily precipitation revealed no statistically significant trends at any station. Daily precipitation characteristics showed significant relationships with various well-known atmospheric circulation patterns (ACPs). In particular, the East Atlantic/West Russia (EA/WR) pattern in summer was the most influential ACP negatively associated with different daily precipitation intensity, frequency and duration indices at all three stations studied.

Abstract

Driving rain is one of the most critical sources of moisture affecting the hygrothermal and durability performance of building envelopes. The estimation of severity in terms of annual driving rain indices using annual and monthly weather data (aaDRI and maDRI respectively) aids towards contemplating potential moisture loads, and hence in the efficient design of buildings in the geographical area of interest. In this study, monthly and annual gridded datasets of wind and rainfall, pertaining to the thirty-year period of 1988-2017 have been used to design a spatially continuous driving rain map for India at 0.5°×0.5°(lat./long.) resolution. The observations reveal that the use of annually averaged data leads to underestimation of the driving rain severity thereby highlighting the inefficiency of a coarser temporal scale. A linear relationship has subsequently been developed to enable refinement of aaDRI into maDRI. The analysis of the monthly driving rain map reveals that the entire western coastal belt and a few regions in the north-eastern part of the country observe high to severe exposure conditions. Furthermore, a trend analysis of the yearly driving rain index values reveals statistically significant decreasing trends over the northern and eastern regions of the country, whereas increasing trends in the shielded regions surrounding central India is observed.