EGGS-WG: An open source global gridded stochastic weather generator derived from ERA5-Land

Abstract. A new open source and freely available stochastic weather generator, the ERA5-land Global Gridded Stochastic Weather Generator (EGGS-WG), is publicly available. This model offers several advancements over existing alternative stochastic weather generators, including the ability to simulate any terrestrial region of the planet, moving from simulating a single site to an entire gridded domain and increasing the temporal resolution of temperature simulation from daily to hourly. EGGS-WG is designed to be as low resource and portable as possible, ensuring ease of use for any potential end user. This paper describes in detail all the principles that are used in the model design and code implementation. Preliminary tests are performed over five climatically distinct regions to confirm the ability of the model to reproduce the behaviour of the ERA5-Land dataset. Precipitation occurrence rates and daily rainfall amounts are shown to be reproduced accurately by the model with a range of attributes investigated, including seasonality, spatial correlations and rainfall spells. Although, there are some clear issues in the simulation of precipitation at the most extreme values. Similar analysis is also performed for the air temperature and dew point temperature, showing stronger agreement than the precipitation data. EGGS-WG is designed with a focus on potential future developments, including support for CMIP6 driven future warming and expansion into simulating other variables provided by the ERA5-Land dataset.