Nepal is one of the most vulnerable countries to climate change impacts. Extreme weather events associated with heavy precipitations are the principal causes of landslides, debris flows and all types of floods disasters in the country, which by causing tremendous losses of life and property affects the socio-economic development. Given the limited availability of knowledge in spatio-temporal distribution of precipitation in Nepal, this study analyses the spatial distribution of monthly and annual precipitation and 1-day extreme precipitation and their trends utilizing a large number of stations (291 stations for the first time) distributed across the country for the period of 1966-2015. This study focuses on the exploration of elevational dependencies of precipitation to demonstrate the effect of topographic heterogeneity caused by the numbers of broad and narrow river valleys and mountain slopes and ridges. Also, this study investigates the relation of 1-day extreme precipitation with mean annual precipitation. Our results show the peak annual precipitation elevation between 2,000 and 3,500 m above sea level, while in contrast 1-day extreme precipitation peaks are found at lower elevation in the southern foothills with its highest intensity in a central region of the country. The occurrence of 10% of mean annual precipitation in a single day has been observed in 75% of the analysed stations which in turn indicates the high likelihoods of initiation of landslides, soil erosions and floods in different parts of the country. There is no definitive countrywide decadal trend in extreme precipitation intensity and occurrence. A station-wise trend clearly shows the increase in extreme precipitation events in western mountainous regions in the recent decades. In other locations, the mixed patterns of station-wise increasing and decreasing trends are found.

Rapid Urbanization, and other anthropogenic activities, have amplified the change in land-use transition from green space to heat emission in built-up areas globally. As a result, there has been an increase in the land surface temperature (LST) causing the Urban Heat Island (UHI) effect, particularly in large cities. The UHI effect poses a serious risk to human health and well-being, magnified in large developing cities with limited resources to cope with such issues. This study focuses on understanding the UHI effect in Kathmandu Valley (KV), Delhi, and Dhaka, three growing cities in South Asia. The UHI effect was evaluated by analyzing the UHI intensity of the city with respect to the surroundings. We found that the central urban area, of all three cities, experienced more heat zones compared to the peri-urban areas. The estimated average surface temperature ranged from 21.1 ∘C in March 2014 to 32.0 ∘C in June 2015 in KV, while Delhi and Dhaka experienced surface temperature variation from 29.7 ∘C in June 2017 to 40.2 ∘C in June 2019 and 23.6 ∘C in March 2017 to 33.2 ∘C in March 2014, respectively. Based on magnitude and variation of LST, highly built-up central KV showed heat island characteristics. In both Delhi and Dhaka, the western regions showed the UHI effect. Overall, this study finds that the UHI zones are more concentrated near the urban business centers with high population density. The results suggest that most areas in these cities have a rising LST trend and are on the verge of being UHI regions. Therefore, it is essential that further detailed assessment is conducted to understand and abate the impact of the temperature variations.

Abstract. Urban flooding causes large economic losses, property damage and loss of lives. The impact of environmental changes, mainly urbanization and climatic change, leads to increased runoff and peak flows which the drainage system must be able to cope with to reduce potential damage and inconvenience. Allowing for detention storage to compliment the conveyance capacity of the drainage system network is one of the approaches to reduce urban floods. Contemporary practice is to design systems against stationary environmental forcings -including design rainfall, landuse, etc. Due to the rapid change in the climate-and the urban environment, this approach is no longer appropriate, and explicit consideration of gradual changes during the life-time of the drainage system is warranted. In this paper, a staged cost optimization tool based on the hydraulic performance of the drainage system is presented. A one dimensional hydraulic model is used for hydraulic evaluation of the network together with a genetic algorithm based optimization tool to determine optimal intervention timings and responses over the analysis period. The model was applied in a case study area in the city of Porto Alegre, Brazil. It was concluded that considerable financial savings and/or additional level of flood-safety can be achieved by approaching the design problem as a staged plan rather than one-off scheme.

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