Abstract. Lakes and reservoirs are ubiquitous across global landscapes, functioning as the largest repository of liquid surface freshwater, hotspots of carbon
cycling, and sentinels of climate change. Although typically considered lentic (hydrologically stationary) environments, lakes are an
integral part of global drainage networks. Through perennial and intermittent hydrological connections, lakes often interact with each other, and
these connections actively affect water mass, quality, and energy balances in both lacustrine and fluvial systems. Deciphering how global lakes are
hydrologically interconnected (or the so-called “lake drainage topology”) is not only important for lake change attribution but also increasingly
critical for discharge, sediment, and carbon modeling. Despite the proliferation of river hydrography data, lakes remain poorly represented in
routing models, partially because there has been no global-scale hydrography dataset tailored to lake drainage basins and networks. Here, we
introduce the global Lake drainage Topology and Catchment database (Lake-TopoCat), which reveals detailed lake hydrography information with
careful consideration of possible multifurcation. Lake-TopoCat contains the outlet(s) and catchment(s) of each lake; the interconnecting reaches
among lakes; and a wide suite of attributes depicting lake drainage topology such as upstream and downstream relationship, drainage distance between
lakes, and a priori drainage type and connectivity with river networks. Using the HydroLAKES v1.0 (Messager et al., 2016) global lake mask, Lake-TopoCat identifies
∼ 1.46 million outlets for ∼ 1.43 million lakes larger than 10 ha and delineates 77.5×106 km2 of lake catchments
covering 57 % of the Earth's landmass except Antarctica. The global lakes are interconnected by ∼ 3 million reaches, derived from MERIT Hydro v1.0.1 (Yamazaki et al., 2019), stretching a total distance of ∼10×106 km, of which ∼ 80 % are shorter than 10 km. With such
unprecedented lake hydrography details, Lake-TopoCat contributes towards a globally coupled lake–river routing model. It may also facilitate a
variety of limnological applications such as attributing water quality from lake scale to basin scale, tracing inter-lake fish migration due to changing
climate, monitoring fluvial–lacustrine connectivity, and improving estimates of terrestrial carbon fluxes. Lake-TopoCat is freely accessible at
https://doi.org/10.5281/zenodo.7916729 (Sikder et al., 2023).