Investigating precipitation growth and decay due to orography using radar rainfall observations in Great Britain

Abstract

This study investigates precipitation growth and decay (GD) characteristics across Great Britain (GB) using a five‐year (2007–2011) weather radar dataset. It aims to enhance radar‐based precipitation forecasting, which typically struggles with decreasing accuracy over lead time due to its inability to account for precipitation GD processes. The research focusses on the orographic effect, where moist air rising over elevated terrain leads to enhanced precipitation. The analysis employs a Lagrangian framework to track precipitation systems and quantifies precipitation GD using a logarithmic approach. Various factors were stratified to understand their influence on precipitation GD patterns, including spatial window sizes and lead times, the direction and speed of storms, and air temperature. The results showed that topography plays a paramount role, with most precipitation growth occurring on windward slopes and decay in leeward areas. The study confirmed a strong directional dependence, with most precipitation in GB originating from the west and southwest, leading to enhanced precipitation in the west part of Wales, the Pennines and Scotland. The results also showed that precipitation growth is enhanced with increasing storm speeds, indicating greater dynamic interaction with terrain. Temperature also modulates precipitation GD, with warmer conditions (above 15°C) showing more widespread precipitation growth. These results provide a framework for incorporating orographic effects and dynamic precipitation evolution into nowcasting models. The study provides insights that are meaningful for future work aimed at improving precipitation GD in nowcasting systems, also critical for flood forecasting and severe‐weather warnings.