Kansas climate basics: Part 5 – Drought, drought changes, and drought cycles
(Editor’s note: The following article is one in a series of articles in the Agronomy eUpdate that examines the historical climate observations in Kansas. The methods used to do this analysis are explained in the introductory article in this series, from eUpdate No. 571, May 20, 2016. – Steve Watson)
Drought and drought changes in Kansas
Droughts are one of the most devastating natural hazards. Severe droughts have had large impacts on Kansas water resources and economies. Kansas is one of the states most prone to drought. The 1930s drought is often considered Kansas’ worst drought on record, which basically means that this was the driest series of years since our instrumental observations starting in late 1800s (although there were sporadic weather observations in the mid-1800s in Kansas). However, tree-ring reconstruction analysis could help us construct long-term drought information over 1,000 years.
Figure 1 displays the western Kansas droughts from the years 1000 to 2000. By going back this far in time, it becomes noticeable that the droughts in 1930s were not the worst in history in terms of either drought duration (consecutive drought period) or drought intensity (the magnitude of drought index). Since 1000, many multiple-year droughts have occurred, ranging from 5 years to 40 years.
Figure 1. Western Kansas annual droughts during past 1,000 years. The vertical axis is the Palmer Drought Severity Index (PDSI). The more negative the PDSI, the drier (orange). On the opposite side, the more positive the PDSI, the wetter (dark green). Data obtained from Cook et al. 2004, Science 306 (5698):1015-1018.
Focusing in on the more recent period of 1895 to 2015 (Figure 2), when a record of instrumental readings is available, it is apparent that the drought events in 1930s and 1950s were the longest and most pronounced of all. These and subsequent droughts have caused significant environmental effects and have had a great impact on Kansas settlement patterns and agricultural operations. Viewed in this historical context, the droughts in 2011 to 2014 in parts of Kansas, while serious, were not anything unusual.
Figure 2. Average PDSI for Kansas growing season (May to October) over 1895 to 2015: (a) Western, (b) Central, and (c) Eastern third of Kansas. The orange shaded areas represent unusual dryness and the green shaded areas represent unusual wetness. The dotted red lines (PDSI = -3) are indicators of severe drought occurrence as defined by PDSI.
Multiple-year drought events have often occurred in Kansas. The state as a whole has not experienced more frequent or more extreme droughts than normal in recent years compared to either the last 1,000 years or the most recent 121-year period. We can parse the PDSI data a bit more finely by dividing the most recent 121-year period into two periods (1895 to 1955 vs. 1956 to 2015) for each of the three regions of Kansas. In doing so, we find only western Kansas had a slightly drier mean and drier median PDSI during the most recent 60-year period when compared to PDSI from 1895 to 1955 (Fig. 3). Both central and eastern Kansas had showed wetter tendencies in the most recent 60-year period. The drought information drawn from Figure 3 was consistent with precipitation trends in Kansas that we reported in this climate series.
Figure 3. Probability density function (PDF) of Palmer Drought Severity Index (PDSI) during 1895-1955 vs. 1956-2015 in western (a), central (b) and eastern Kansas (c), respectively. The negative numbers to the left of “0” on the x axis represent drier-than-average conditions; the positive numbers to the right of “0” represent wetter-than-average conditions. Only in western Kansas is there a slightly drier-than-average trend in the 1956 to 2015 period (red lines) compared to the 1895 to 1955 period (blue lines). In central and eastern Kansas, the trend in the most recent time period has been slightly wetter-than-average.
Xiaomao Lin, State Climatologist, Department of Agronomy
John Harrington Jr., Department of Geography
Ignacio Ciampitti, Crop Production and Cropping Systems Specialist
Mary Knapp, Weather Data Library