Weather or not—Global climate databases: Reliable on tropical mountains?

RESEARCH ARTICLE Weather or not—Global climate databases: Reliable on tropical mountains? Andreas HempID1,2*, Judith Hemp3 1 Department of Plant Systematics, University of Bayreuth, Bayreuth, Germany, 2 Waldkunde-Institut Eberswalde, Eberswalde, Germany, 3 Friedrich-Alexander-Universita¨ t Erlangen-Nu¨rnberg (FAU), Erlangen, Germany * andreas.hemp@uni-bayreuth.de Abstract Global, spatially interpolated climate datasets such as WorldClim and CHELSA, widely used in research, are based on station data, which are rare in tropical mountains. However, such biodiversity hotspots are of high ecological interest and require accurate data. There- fore, the quality of such gridded datasets needs to be assessed. This poses a kind of dilemma, as proving the reliability of these potentially weakly modelled data is usually not possible due to the lack of stations. Using a unique climate dataset with 170 stations, mainly from the montane and alpine zones of sixteen mountains in Tanzania including Kilimanjaro, we show that the accuracy of such datasets is very poor. Not only is the maximum amount of mean annual precipitation drastically underestimated (partly more than 50%), but also the elevation of the precipitation maximum deviates up to 850m. Our results show that, at least in tropical regions, they should be used with greater caution than before. Introduction Global, spatially interpolated climate data on grids are widely used in scientific research in var- ious disciplines, including ecology, biodiversity, conservation and climate change [1,2]. Such

gridded datasets use global or continental networks of weather stations, e.g. GHCN-D [3] or HSM-SIEREM [4] for their modelling approaches. There are several gridded climate reanalysis datasets merging satellite and station data (e.g. CRU [5] or ERA5 [6]) with a rather coarse spa- tial resolution between 0.25 and 1 degree (which corresponds to about 28 to 100 km in the tropics). However, this resolution is much too coarse to capture orographic precipitation pat- terns in complex terrain [7,8]. Furthermore, for many questions and applications in environ- mental research and ecology, climate data with higher resolution is essential [2]. Databases such as WorldClim [9] (WC) provide free access to downscaled climate data with a spatial resolution of 30 arc seconds; this corresponds to about 0.86 km2 at the equator and is commonly referred to as "1-km" or "high" or "very high" resolution [2,7]. WC provides a range of climate variables derived from weather station records and other sources, such as tem- perature, precipitation, solar radiation, wind speed and humidity. WorldClim’s strengths include its comprehensive coverage, ease of use and availability of different spatial resolutions. CHELSA (Climatologies at High Resolution for the Earth’s Land Surface Area [10] (C) is PLOS ONE PLOS ONE | https://doi.org/10.1371/journal.pone.0299363 March 13, 2024 1 / 12 a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 OPEN ACCESS Citation: Hemp A, Hemp J (2024) Weather or not —Global climate databases: Reliable on tropical mountains? PLoS ONE 19(3): e0299363. https://

doi.org/10.1371/journal.pone.0299363 Editor: Nir Y. Krakauer, City College of New York, UNITED STATES Received: November 15, 2023 Accepted: February 8, 2024 Published: March 13, 2024 Copyright: © 2024 Hemp, Hemp. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: The datasets generated and analysed during the current study are available in the PANGAEA repository (Link: https://doi.pangaea.de/10.1594/PANGAEA. 942806). However, some of the data used in this study belong to private owners of the Tanzania Meteorological Authority (TMA). To access these data, please contact the TMA directly at the following address: Tanzania Meteorological Authority (TMA) University of Dodoma, Administration Block, Department of Computer Science and Intuitive Education, 1 CIVE Street, P.O Box 27, 41218 DODOMA. Telephone: +255 26