Coherence of global hydroclimate classification systems

Authors: Pisarello, Kathryn; JAWITZ, JAMES - University Of Florida

Submitted to: Hydrology and Earth System Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/25/2021
Publication Date: 12/6/2021
Citation: Pisarello, K., Jawitz, J.W. 2021. Coherence of global hydroclimate classification systems. Hydrology and Earth System Sciences. https://doi.org/10.5194/hess-25-6173-2021.
DOI: https://doi.org/10.5194/hess-25-6173-2021

Interpretive Summary: Categorizing regions of the world according to climate-hydrology interactions is a valuable planning tool for assessing the effects of water availability on multiple societal systems, such as food production, flood control, road and bridge design, and economic development. Existing classification systems are complex, require large amounts of data, and often do not result in contiguous regions that match climate-water source areas. Compared to the currently most used classification system that requires 24 data parameters, we developed the Water-Energy Clustering Classification (WEC) system as an alternative that requires only two data parameters to provide equal or improved coherence (i.e., higher within-zone similarity) for most variables reflective of climate-water interactions. The WEC system supplies a simplified framework to inform regional-to-national strategies that assess risk and risk mitigation costs resulting from potential future hydroclimate changes.

Technical Abstract: Climate classification systems are useful for investigating future climate scenarios, water availability, and even socioeconomic indicators as they relate to climate dynamics. There are several classification systems that apply water and energy variables to create zone boundaries, although there has yet to be a simultaneous comparison of the structure and function of multiple existing climate classification schemes. Moreover, there are presently no classification frameworks that include evapotranspiration (ET) rates as a governing principle. Here, we developed a new system based on precipitation and potential evapotranspiration rates, as well as three systems based on ET rates, which were all compared against four previously established climate classification systems. The within-zone similarity, or coherence, of several long-term hydroclimate variables was evaluated for each system based on the premise that the interpretation and application of a classification framework should correspond to the variables that are most coherent. Additionally, the shape complexity of zone boundaries was assessed for each system, assuming zone boundaries should be drawn efficiently such that shape simplicity and hydroclimate coherence are balanced for meaningful boundary implementation. The most frequently used climate classification system, K'ppen-Geiger, generally had high hydroclimate coherence but also had high shape complexity. When compared to the K'ppen-Geiger framework, the Water-Energy Clustering classification system introduced here showed overall improved or equivalent coherence for hydroclimate variables, yielded lower spatial complexity, and required only two, compared to 24, parameters for its construction.