Just how much rain qualifies as a toad-strangler?
Have you heard the term “Toad-strangler”? For those unfamiliar with the phrase, it means a very heavy rain – enough to strangle a toad. That picturesque phrase very nicely captures the deluge of rain experienced throughout much of eastern and central Kansas on Friday, May 15. The Kansas Mesonet station at Parsons reported 4.70 inches on the May 15, 2020. Seven other weather stations, including CoCoRaHS and NWS Coop stations reported over 3 inches for the date
While the Parsons total was well above the 95-year average single-day rain of 3.58”, it is not the largest amount of rain received. The highest 1-day rainfall total for Parsons was 7.48” of rain received on June 22, 1948 (Figure 1). Other stations in the Southeast Division received even more that day, with the greatest amount reported at Altamont at 10.55 inches. That year Parsons had total rainfall of 44.45”, just slightly above the 95-year average of 41.5”. The Southeast Divisional average for that year was 40.13”.
Figure 1. Greatest daily rainfall totals at Parsons. The orange line is the average single-day rainfall maximum at 3.58”.
Reviewing records from currently active stations, the largest daily rainfall total on record occurred at Fort Scott (Figure 2). They reported 12.50” on September 15, 1998. While the summer months have the largest monthly totals and the most extreme rain events, of the 957 currently active stations, 242 have their record rainfall days in the fall (September - November). In many cases, the large rainfall totals come from a highly localized storm with very little movement. While the highest single-day rainfall total roughly follows the average annual precipitation pattern, stations in central and northern portions of Kansas also receive high rain events.
Figure 2. Maximum daily precipitation values. Source: Kansas Weather Data Library.
Unfortunately, while these intense rain events create their own problem, they do not tell the whole story. A heavy rain event might produce localized flash flooding, but the waters usually recede quickly. If the events are part of an overall wet pattern, runoff may be greater and the flooding will persist longer.
Soil moisture is one of the factors that affects water infiltration into the soil. Dry soils will have a faster infiltration rate at first, which slows as soil pores become occupied by water. Soil texture, at the surface and in horizons below the surface, also affects infiltration rate, as does management. Crop residue protects the soil surface from the impact of raindrops and can help keep the soil from crusting off. Intense rain events can quickly exceed a soils infiltration capacity, as well as move soil at the surface sealing off macropores leading to greater amounts of runoff. Residue management, cover crops and no-tillage are recommended best management practices that protect the soil surface and reduce the amount of sediment lost as water runs off (Figure 3). Current streamflow levels are high in the eastern areas of the state (Figure 4). Little additional rainfall would be needed to produce more widespread and persistent flooding.
Figure 3. Adding cover crops to a no-tilled wheat-grain sorghum led to increased ponded infiltration rates. This was measured 15 years after the study started. Adapted from Blanco-Canqui, H., Claassen, M. M., & Presley, D. R. (2012). Summer cover crops fix nitrogen, increase crop yield and improve soil-crop relationships. Agronomy Journal, 104(1), 137-147.
Figure 4. Current river levels in Kansas. Source: USGS
The Southeast Division continues with very high rainfall in 2020, with the 10th wettest start to the year since 1895. With the accumulation through Thursday, May 28, Parsons has the wettest start to the year since 1925 (Figure 5).
Figure 5. Cumulative precipitation at Parsons. Graph created by Gretchen Sassenrath, K-State Research and Extension.
Gretchen Sassenrath, Southeast Area Agronomist
DeAnn Presley, Environmental Soil Science and Management
Peter Tomlinson, Environmental Quality Extension Specialist
Xiaomao Lin, State Climatologist
Mary Knapp, Assistant State Climatologist