MATCHA, a novel regional hydroclimate-chemical reanalysis: System description and evaluation

We present MATCHA (Model for Atmospheric Transport and Chemistry in Asia), a 17-year (2003–2019) regional hydroclimate-chemical reanalysis for Asia (58–140° E, 4– 40° N) at 12 km resolution. MATCHA couples the Weather Research and Forecasting model with Chemistry (WRF-Chem), Community Land Model (CLM), and SNow, Ice, and Aerosol Radiative (SNICAR) model, and assimilates aerosol optical depth (AOD) from the Moderate Resolution Imaging Spectroradiometer (MODIS) and carbon monoxide (CO) profiles from the Measurement of Pollution in the Troposphere (MOPITT) every three hours, to explicitly represent interactions between atmospheric composition and regional hydroclimate (including aerosol-snowpack interactions) across High Mountain Asia (HMA). MATCHA comprises hourly surface and column-integrated fields and 3-hourly three-dimensional fields across different light-absorbing aerosol species, e.g., black carbon (BC), dust, and brown carbon (BrC), trace gases, and a broad set of meteorological, hydrological, and land-surface variables over the region. We evaluate 12 key variables in the reanalysis against in-situ and satellite observations. Surface and upper-air meteorology is reproduced well, with Kling-Gupta efficiencies (KGEs) of 0.65 to 1, although high-elevation regions show a persistent winter cold and dry bias and too-strong surface winds. Snow cover fraction seasonality is captured across the major glacier regions, with a slight underestimation during snowmelt, and daily precipitation agrees most closely during the monsoon (KGE up to 0.6). MATCHA reproduces the spatial and seasonal patterns of AOD and single scattering albedo (SSA) at 550 nm but overestimates summer AOD over India and Southeast Asia; surface PM_2.5 and PM₁₀ are biased high and surface CO is underestimated relative to observations. A distinguishing feature of MATCHA is a set of tagged BC tracers that attribute concentrations to specific emission sectors and source regions. These tracers show anthropogenic BC peaking in winter (Chinese sources over eastern and northern HMA, Indian sources over the west and center) and biomass-burning BC dominating in March-April. MATCHA is the first high-resolution reanalysis over HMA to fully couple aerosols, radiation, and snow. It supports research on aerosol-cryosphere feedbacks, air quality, and hydroclimate over a region where observations are sparse, and its resolution and 17-year length make it suitable as a training set for statistical and machine-learning models. The dataset is publicly available at https://doi.org/10.5067/CG4OT8DJX2Z7 (Kumar et al., 2024).