Heavy rainfall forecasting for Dehradun capital city during monsoon season 2020

Abstract

Dehradun city is Uttarakhand's capital and part of the doon valley, which lies between the Himalayas and the Shivaliks. India Meteorological Department has undertaken the Impact Based Forecasting (IBF) of heavy rainfall events for capital/major cities on an experimental basis from the monsoon season 2020. With the improvement in meteorological observation & monitoring network of Uttarakhand and short & medium range Numerical Weather Prediction (NWP) model outputs, it has become possible to provide impact-based forecast at a very small spatial scale with good accuracy. With the help of a dense network of 5 General Packet Radio Service (GPRS) based Automatic Weather Stations (AWS) & 2 Automatic Rain Gauges (ARG) within a 20 Km radius of Dehradun city center, it has become possible to capture & monitor these events. The spatial analysis of these events suggests that the local orographic features rather than large-scale synoptic features played a major role in heavy rainfalls over Dehradun city. The Heidke skill score of 0.63 and 100% probability of detection is found for the capital city forecast of Dehradun. The presence of monsoon trough to the north of its normal position, a cyclonic circulation south of Uttarakhand over Haryana or East-Rajasthan or West Uttar Pradesh and a Western disturbance around 70°E were found to be the synoptic systems favorable for the occurrence of heavy rainfall in Dehradun city. The occasional strong south-westerly wind flow from the Arabian Sea converging over the foothills of the Western Himalayas is also found to be responsible for the heavy downpour.

Western disturbances and climate variability: a review of recent developments

“…WDs are often thought of as occurring only during the winter months, but a long list of case studies (e.g. Yadav et al, 2017a;Gupta et al, 2023;Thapliyal and Singh, 2023a) and recorded interactions with the summer monsoon (e.g. Pisharoty and Desai, 1956;Chevuturi and Dimri, 2016;Hunt et al, 2021) show that they can occur at any time of year.…”

“…Further, they showed that winter landslides in the Upper Indus Basin that could not be linked to WDs were associated with local, smaller-scale, orographically-driven cloudbursts. The interaction between a WD and a tropical low brought record-breaking rainfall and widespread landslides to Uttarakhand in October 2021 (Thapliyal and Singh, 2023a). Similarly, in bringing heavy snowfall to the Himalayas in both the winter and pre-monsoon seasons (and occasionally during the summer monsoon itself), WDs are a potential driver of increased avalanche risk (Hara et al, 2004), especially given most avalanches occur in the western Himalaya between January and May (Ballesteros-Cánovas et al, 2018).…”

“…Perhaps the most notorious example occurred in June 2013, when a WD interacted with a monsoon low-pressure system, resulting in devastating floods over Uttarakhand (Kotal et al, 2014). Other cases have been noted, with Uttarakhand seemingly the most common region impacted (Thapliyal and Singh, 2023b). Majid et al (2023) showed that floods in the Indus Basin in September 2014 were linked the accumulated effect of several WDs interacting with the summer monsoon.…”

Flash flood dynamics in the foothills of NW Himalaya: Insights into hydrological and geological controls

“…Poorly planned urban growth further exacerbates the impact of excessive rainfall on lives and property, as cities struggle to accommodate growing populations, disrupting ecosystems (Chadchan and Shankar, 2012;Thapliyal and Panwar, 2020). This expansion has far-reaching environmental consequences at regional and global scales (Bhat et al, 2017;Thapliyal and Panwar, 2020). In the case of Dehradun, construction in ecologically sensitive areas, like riverbanks, terraces, and unstable slopes, increases ood risks (Khanduri and Sajwan, 2019;Sati and Kumar, 2022).…”

“…Changes in land use and cover, along with deforestation and increased concrete surfaces, lead to reduced in ltration and increased surface runoff (Sati 2013). Poorly planned urban growth further exacerbates the impact of excessive rainfall on lives and property, as cities struggle to accommodate growing populations, disrupting ecosystems (Chadchan and Shankar, 2012;Thapliyal and Panwar, 2020). This expansion has far-reaching environmental consequences at regional and global scales (Bhat et al, 2017;Thapliyal and Panwar, 2020).…”