> For the complete documentation index, see [llms.txt](https://hydrosense.gitbook.io/ildas/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://hydrosense.gitbook.io/ildas/technical/model-forcings.md). # Model Forcings Meteorological forcings provide the boundary conditions in land surface models (LSM). ILDAS requires 7 meteorological forcings variables: 1. Rainfall Rate 2. Near Surface Air Temperature 3. Near Surface Specific Humidity 4. Wind 5. Surface Pressure 6. Incident Shortwave Radiation 7. Incident Longwave Radiation The forcings variables used by ILDAS are obtained from the following products: **IMD Gridded Precipitation:** The Indian Meteorological Department (IMD) gridded precipitation data is generated by spatially interpolating data from 6995 gauged stations. The stations from various sources include IMD observatory stations, hydro-meteorological observatories, and Agromet observatories (Pai et al., 2014) across India. Based on (Shepard, 1968), the IMD gridded product is constructed using an inverse distance weighting system with localized directional effects and barriers. IMD gridded data with 0.25⁰ spatial resolution is accessible from 1981 to the present. Similar to CHIRPS, MERRA-2 is used for other required meteorological variables for IMD gridded precipitation as well. Data availability: **MERRA2:** The Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2; (Gelaro et al., 2017) is an upgraded version of MERRA, which includes the recent advances made in the assimilation systems by NASA's Global Modeling and Assimilation Office (GMAO) that can assimilate microwave observations, hyperspectral radiance and other datatypes. MERRA-2 product is available at a spatial resolution of 0.25⁰×0.625⁰ globally at an hourly time step. The product has been available since 1980 and is updated operationally with about one week of latency. Data availability: **ERA5** ECMWF's ERA-5 (ERA-5; Hersbach at al., 2020) is a new global reanalysis dataset that builds upon the earlier ERA-Interim reanalysis. The dataset is available from 1959 to the present at a spatial resolution of 0.25° and hourly timestep. ERA-5 uses a 10-member ensemble with a 12-hour 4D-Var data assimilation method to include various reprocessed datasets. The dataset is available in preliminary form at 5 days latency to real-time, and the final quality-assured product is released with a latency of 2 months. Data availability: **CHIRPS:** Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS; Funk et al., 2015) is a quasi-global precipitation dataset derived from global Cold Cloud Duration (CCD) rainfall estimates calibrated using Tropical Rainfall Measuring Mission Multi-Satellite Precipitation Analysis version 7 (TMPA 3B42 v7). CHIRPS precipitation estimates integrate active radar satellite systems and in-situ gauge station data with a 3-week lag. From 1981 until the present, CHIRPS data is available with a spatial resolution of 0.05⁰. While using CHIRPS precipitation data as an input, other required meteorological variables are specified from MERRA-2. Data availability: