Global warming enables atmosphere to hold more water and accelerates the global water cycle. The warmer air provides more moisture to rainfall events and leads to extreme short-duration rainfall increasing in magnitude and frequency worldwide.
For these increasing short-duration rainfall events, in addition to the water infiltrates into the soil and urban drainage system, the remaining large amount of water flowing on the ground triggers the flooding and waterlogging disasters in urban areas and various hydrologic and geologic hazards in natural areas. The huge amount of runoff in a short time carries various pollutants and pathogenic bacteria, which may spread different diseases and cause social panic. Thus, it’s important to accurately simulate the infiltration process of short-duration rainfall.
Influenced by soil properties, initial water content, rainfall type and surrounding environments, the infiltration process of natural soils fluctuate, e.g., the observed fluctuated infiltration process in Figure 1. Though many infiltration models have developed, little or no model can well simulate the infiltration fluctuation, which subsequently causes great uncertainty in the simulation of water environmental pollution.
In order to reduce the hydrologic disasters caused by short-duration rainfall, accurately simulate the non-point source pollution process and meet the needs of managing the water resources and water environment, Yang’s research group specifically developed a simple analytical infiltration model for short-duration rainfall, i.e., the Short-duration Infiltration Process model (SHIP model) [1]. SHIP model consists of three sub-models, i.e., SHIP (high), SHIP (middle) and SHIP (low) models, and SHIP (high) and (low) models construct an infiltration range.
SHIP (high) model is the upper boundary of the infiltration range and it resembles the “ceiling” of infiltration fluctuation. SHIP (low) model is the lower boundary of infiltration range and it resembles the “floor” of infiltration fluctuation. SHIP (middle) model gives the optimal approximation of infiltration processes. As shown in Figure 1, the observed infiltration process fluctuated between SHIP (high) and SHIP (low) models and the infiltration range simulated by SHIP model almost completely cover the observed infiltration fluctuation.
Figure 1. The observed and SHIP model simulated infiltration process of a short-duration rainfall.
For a complete rainfall infiltration process, the soil has large infiltration capacity and all the rainfall infiltrates into the soil at the beginning of the rainfall. Runoff generates at the time when the rainfall intensity is greater than the infiltration capacity. The transition time from pre-ponding to post-ponding can be estimated by the time compression technique. Coupling the time compression technique, SHIP model can completely simulate the infiltration process from pre-ponding to post-ponding.
SHIP model has provided robust solutions for short-duration rainfall infiltration in our experiments. However, to further develop it for natural and general rainfall situations, future studies should consider the following improvements. Firstly, the time scale of short-duration rainfall is still arguable and it needs to be defined mathematically. For different watersheds and precipitation types, the time scale of short-duration rainfall varies from several hours to several weeks. To better distinguish and use different infiltration models, more infiltration models need to be compared at various time and space scales.
Secondly, SHIP model needs to be coupled into hydrological models for infiltration calculations. Combining the consideration of other hydrologic processes, the geologic and ecologic conditions and complex human engineering measures, SHIP model will be developed to simulate the infiltration processes more accurately, e.g., considering the time-variant thickness of water above the soil surface or the influence of plant roots. We hope the SHIP model will be developed to solve the related hydrology and water environment problems for everyone.
These findings are described in the article entitled A simple analytical infiltration model for short-duration rainfall, recently published in the journal Journal of Hydrology. This work was conducted by Kaiwen Wang, Xiaomang Liu, and Changming Liu from the Chinese Academy of Sciences, and Xiaohua Yang from Beijing Normal University.
Reference:
- Wang, K., Yang, X., Liu, X., & Liu, C. (2017). A simple analytical infiltration model for short-duration rainfall. Journal of Hydrology, 555, 141-154.