Drought
Table of Contents
The National Oceanic and Atmospheric Administration defines drought as a deficiency in precipitation over an extended period, usually a season or more, resulting in a water shortage causing adverse impacts on vegetation, animals, and/or people. It is a normal, recurrent feature of climate that occurs in virtually all climate zones, from very wet to very dry. Drought is a temporary aberration from normal climatic conditions, thus it can vary significantly from one region to another. Drought is different than aridity, which is a permanent feature of climate in regions where low precipitation is the norm, as in a desert.
Human factors, such as water demand and water management, can exacerbate the impact that drought has on a region. Because of the interplay between a natural drought event and various human factors, drought means different things to different people. In practice, drought is defined in a number of ways that reflect various perspectives and interests.
Description + Extent
Types of Drought
- Meteorological drought: A period of abnormally dry weather sufficiently prolonged for the lack of water to cause serious hydrologic imbalance in the affected area.
- Agricultural drought: A climatic excursion involving a shortage of precipitation sufficient to adversely affect crop production or range production.
- Hydrologic drought: A period of below average water content in streams, reservoirs, groundwater aquifers, lakes and soils.
- Socioeconomic drought: Socioeconomic drought refers to the situation that occurs when water shortages begin to effect people and their lives. It associates economic good with the elements of meteorological, agricultural, and hydrological drought.
Understanding Drought
Part of the difficulty in detecting drought is in the lack of an obvious onset of drought conditions. A drought develops slowly and can appear to mimic a normal spell of dry weather in the summer, a time of the year when dry weather is accepted and expected. Short-term rainfall shortages create problems for agricultural crops, livestock, urban landscapes, and other activities that depend on stored soil moisture between rainfall events.
Despite all of the problems that droughts cause, drought has proven to be difficult to define. There is no universally accepted definition because drought, unlike flooding for example, is not a distinct event. Additionally, drought is often the result of many complex factors and has no well- defined start or end. The impacts of drought may again vary by affected sector, thus making definitions of drought specific to particular situations.
U.S. Drought Monitor
The U.S. Drought Monitor is one way to understand drought. Blending qualitative and quantitative data, it provides a weekly assessment of drought conditions across the U.S. It uses numeric inputs such as the Palmer Drought Severity Index, the Standardized Precipitation Index, and other climatological inputs; the Keech-Byram Drought Index for fire, satellite-based assessments of vegetation health, and various indicators of soil moisture; and hydrologic data, particularly in the West, such as the Surface Water Supply Index and snowpack. It also incorporates empirical evidence from 450 observers across the U.S. including state climatologists, National Weather Service staff, extension agents, and hydrologists.
A description of each category is available below:
Source: U.S. Drought Monitor
Location + Past events
Drought Monitor
The following table displays the number of weeks in D2 (moderate) and D3 (severe) by county. This data is not available at the city level.
USDA Drought Declaration
The USDA issues drought declarations for counties if:
- Their governor makes a request in writing to the Secretary of Agriculture
- If the state can show that the counties in question experienced at least a 30% production loss for at least one crops.
Since 2000, the USDA has issued two drought disaster declarations for KIPDA counties.
- 2012: Bullitt, Henry, Oldham, Shelby, Spencer, and Trimble counties
- 2019: Bullitt and Spencer counties
Probability
Occurence
The KIPDA region, as a whole, experienced 239 weeks of moderate to severe drought over a 21-year period. The following break down is by county:
- Bullitt: 44 total weeks in drought/21 years (1,092 weeks) = 4% chance of drought happening in any given week.
- Henry: 46 total weeks in drought/21 years (1,092 weeks) =4% chance of drought. happening in any given week.
- Oldham: 47 total weeks in drought/21 years (1,092 weeks) =4% chance of drought happening in a given week.
- Shelby: 47 total weeks in drought/21 years (1,092 weeks)= 4% chance of drought happening in a given week.
- Spencer: 47 total weeks in drought/21 years (1,092 weeks)=4% chance of drought happening in a given week.
- Trimble: 52 total weeks in drought/21 years (1,092 weeks)=5% chance of drought happening in a given week
Therefore, each county in the KIPDA region demonstrates between a 4-5% chance of experiencing drought in any given week.
Climate Change
The results of a 2010 study on drought were uncertain for the Kentuckiana region; depending on the level of emissions released in the future, drought could either decrease or increase in frequency in the region. [1] Another 2010 study, focused on the Midwest, found much of the same. It appears as though the increased precipitation in the region will offset the possibility of drought. [2] The effect of climate change on the intensity and duration of droughts in the region is still relatively unknown. Illinois’ state climatologist, Jim Angel, thinks that the Midwest should be more worried about short flash droughts in the summer than the traditionally thought of long-term drought. [3]
Kentucky has been experiencing drought conditions more frequently in the past few years. In September of 2019, the Kentucky Energy and Environment Cabinet declared the entire state to be under either Level 1 or 2 drought conditions, with the Kentuckiana region being under Level 1. [4]
Overall Probability
Overall, the KIPDA HMP ranks the probability of an event for the region as high. While the impact of climate change on drought in the region is unclear, it should be noted that climate change intensifies extremes, such as drought. While the KIPDA region does not experience intense droughts like the western U.S., it still experiences a high probability of a drought occurring in any given year.
Impact
In the KIPDA region, the primary impact of drought is on agriculture. Drought is likely to occur on an annual basis; however, such a drought is likely to impact agriculture – not water supply or access. Therefore, the impact of drought in the KIPDA region can be understood through agricultural impacts – such as crop insurance loss data.
- Prolonged periods of drought can cause severe water shortage. Severe water shortage may force utilities to suggest or require that their users consume less water. They could also raise fees for water.
- Severe drought can cause crops to fail, which can limit farmers’ income and potentially impact the economy of rural communities. This could also cause the price of crops to rise.
- Drought typically does not cause harm to the built environment. However, it can cause farmers to lose crops and livestock.
- Environmental degradation via erosion and ecological damage can be additional results of drought. As moisture in topsoil dissipates and the ground becomes dryer, the susceptibility to windblown erosion increases. In prolonged drought situations loss of habitat for certain species native to that particular environment is possible.
- Prolonged drought conditions may also result in loss of food sources for certain species.
Crop Loss
This dashboard displays the indemnity amount, which represents the dollar amount of yield loss due to drought. The dashboard also shows the number of acres that were impacted by drought. [5]
Source: USDA Risk Management Agency
Vulnerability
Soil Susceptibility
Soil’s susceptibility to drought varies due to a myriad of factors. The map below depicts vulnerability to drought based on soil type from a moisture retention and availability perspective. For example a shallow fragipan limits the depth of the soil making it more vulnerable to moisture loss. Grey areas indicate that no soil data was available to lakes, heavily urbanized areas, or strip mining. Susceptibility to Drought Scores were established using the criteria of infiltration, water movement, and water supply for the soils defined in the NRCS Soil Surveys that encompass the state. [6]
Soils Susceptibility to Drought in KIPDA Region
Source: Commonwealth of Kentucky Hazard Mitigation Plan, 2018
You can access the online version here.
Public Water System Vulnerability
The Commonwealth of Kentucky’s 2018 Hazard Mitigation Plan created a public water system vulnerability scoring system for Kentucky. Water systems may be more vulnerable to drought due to percent leakage loss, water source, and more. This map clips the state’s public water system vulnerability rating to the KIPDA region. [6]
The map indicates that the KIPDA region’s public water systems as a whole exhibit a low vulnerability to drought.
- Primary Source Score: Created by taking a system’s main source and assigning a score (from
1 to 3 with 3 being the least vulnerable) based on how drought vulnerable that source.
Stream flow variabilities, lake characteristics, historical documents, and the systems demand
compared to the size of the source, were taken into consideration. Sources that have
experienced issues in the past or have the potential to experience a shortage in a moderate
drought were given a high-risk score (1 or 1.5). Sources that have the potential to experience
a shortage in a significant drought were given a moderate risk score (2 or 2.5). Sources that
are essentially drought invulnerable were given a low risk score (3). Systems that purchase
water were scored based upon the score of the system(s) the water is purchased from. - All Sources Score: Created by taking into account all the sources that a system uses. This
includes stream/rivers used for a pump store, secondary wells, etc. Systems were then
scored using the same criteria as used above. - Supply Score: Created by taking the All Sources score and also including management into
the scoring. This including interconnections with other systems proactiveness of system
staff, city officials, etc. in previous droughts or current planning. Systems that have a source
score of 3 were not scored on management. - Leakage Loss: Percent leakage loss is one of two factors that go into creating the
infrastructure score. Percent leakage loss was calculated using numbers found in WRIS and
SDWIS MORs. Percent leakage loss is the percent of treated water produced by a system
that is unaccounted for. This can be caused by several things including leakage from pipes,
slow running meters, and theft. For this analysis, it is being assumed that a large portion of
the unaccounted-for water is due to leakage from pipes. - Distribution Lines 3 Inches or Less: Calculated using the miles of 3” lines or less in a system
divided by the total miles of lines in a system. - Public Water System Hazard: Is calculated by averaging the Supply Vulnerability Score and
the Infrastructure Score, which is the average of Leakage Loss and 3-inch Lines. The score is
weighted for Supply Vulnerability.
Land Use
As mentioned before, agriculture experiences the greatest impact from drought in the KIPDA region. Therefore, a county’s land use can be a good indicator of vulnerability. Click on the button below to view the 2019 National Land Cover Database clipped to the KIPDA HMP counties. The National Land Cover Database provides nationwide data on land cover and land cover change at a 30m resolution with a 16-class legend based on a modified Anderson Level II classification system. NLCD 2019 represents the latest evolution of NLCD land cover products focused on providing innovative land cover and land cover change data for the Nation. [7]
Hazard Vulnerability Summary analysis
The KIPDA Region has a near uniform risk of low to moderate drought happening annually. However, factors, such as soil composition, acres of agricultural land, and water loss, make certain communities within the region more vulnerable to drought.
- Bullitt County’s public water system demonstrates low vulnerability to drought.
- The soil susceptibility map indicates that large swaths of Bullitt County’s soil experience low to moderately low susceptibility to drought.
- During intense drought years of 2012 and 2019, the county showed crop losses less than $600,000.
- It was one of only two counties in the KIPDA region that received an official drought declaration from the USDA in 2019.
Overall, Bullitt County has a low to moderate vulnerability to drought. Because drought is a non-spatial hazard, this same analysis can be applied to its respective cities – Fox Chase, Hebron Estates, Hillview, Hunters Hollow, Lebanon Junction, Mount Washington, Pioneer Village, and Shepherdsville.
- Henry County’s public water system demonstrates low vulnerability to drought.
- The soil susceptibility map indicates that parts of Henry County are highly vulnerable to drought. However, Henry County’s areas of high soil susceptibility tend to coincide with forested land and not agricultural land.
- Henry County did experience substantial acreage and crop losses in proportion to its crop area in 2011 (over $1 million). This was not a notable year for any other county.
Overall, Henry County has a low to moderate vulnerability to drought. Because drought is a non-spatial hazard, this same analysis can be applied to its respective cities – Campbellsburg, Eminence, New Castle, Pleasureville, and Smithfield.
- Oldham County’s public water system demonstrates low vulnerability to drought.
- The soil susceptibility map indicates that large swaths of Oldham County’s soil experience low to moderately low susceptibility to drought.
- During intense drought years of 2012 and 2019, the county showed crop losses less than $500,000.
Overall, Oldham County has a low to moderate vulnerability to drought. Because drought is a non-spatial hazard, this same analysis can be applied to its respective cities – Crestwood, Goshen, La Grange, Orchard Grass Hills, Pewee Valley, and River Bluff.
- While the majority of Shelby County is located within a low public water system vulnerability, its primary city, Shelbyville, demonstrates moderate public water system vulnerability.
- The soil susceptibility map indicates that Shelby County does not experience high soil susceptibility to drought.
- During intense drought years of 2012 and 2019, Shelby County showed crop losses between $2 – $3 million dollars, the highest in the KIPDA region.
- The National Land Cover map indicates that Shelby County has more cropland than other counties, which makes it uniquely vulnerable to drought.
Overall Shelby County has a moderate vulnerability to drought. Shelbyville demonstrates a moderate vulnerability to drought as well because of its higher water system vulnerability. On the other hand, Simpsonville, experiences low vulnerability because it has very limited crop land and experiences low water system vulnerability.
- Spencer County’s public water system demonstrates low vulnerability to drought.
- The soil susceptibility map indicates that Spencer County does not experience high soil susceptibility to drought.
- Spencer County experienced just under $700,000 in crop loss during the 2019 drought.
- Spencer was one of only two counties that received a USDA drought declaration in 2019.
Overall, Spencer County has a low vulnerability to drought. Because drought is a non-spatial hazard, this same analysis can be applied to its only city – Taylorsville.
- Trimble County’s public water system demonstrates low vulnerability to drought.
- The soil susceptibility map indicates that parts of Trimble County are highly vulnerable to drought. Higher soil susceptibility occurs in areas of Trimble County that are forested or used for hay/pasture.
- Trimble County experienced approximately $500,000 in crop losses during the 2012 drought; however, while other counties saw substantial crop losses in 2019, crop losses in Trimble County were less than $200,000.
Overall, Trimble County has a low to moderate vulnerability to drought. Because drought is a non-spatial hazard, this same analysis can be applied to its respective cities – Bedford and Milton.
References
[1] Strzepek, K., Yohe, G., Neumann, J., & Boehlert, B. (2010). Characterizing changes in drought risk for the United States from climate change. Environmental Research Letters, 5(4), 044012. doi: 10.1088/1748-9326/5/4/044012
[2] Trenberth, K. E., Dai, A., Schrier, G. V., Jones, P. D., Barichivich, J., Briffa, K. R., & Shef\ield, J. (2013). Global warming and changes in drought. Nature Climate Change, 4(1), 17-22. doi:10.1038/nclimate2067
[3] .Mishra, V., Cherkauer, K. A., & Shukla, S. (2010). Assessment of Drought due to Historic Climate Variability and Projected Future Climate Change in the Midwestern United States. Journal of Hydrometeorology, 11(1), 46-68. doi: 10.1175/2009jhm1156.1
[4] Kratzenberg, J., & *, N. (2019, October 03). Drought declarations issued throughout Kentucky. Retrieved July 24, 2020, from https:// www.lanereport.com/117661/2019/10/drought-declarations-issued- throughout-kentucky/
[5] USDA Risk Management Agency (2021). Cause of loss. [Data set]. Retrieved from https://www.rma.usda.gov/en/Information-Tools/Summary-of-Business/Cause-of-Loss
[6] Kentucky Emergency Management Agency (2018). 2018 Kentucky Hazard Mitigation Plan: S3-S6, Risk Assessment, Hazard Identification, Drought, Revised Submittal. Retrieved from https://kyem.ky.gov/recovery/Pages/Recovery-Document-Library.aspx
[7] Multi-Resolution Land Characteristics Consortium (2021). NLCD 2019 Land Cover. [Data set]. National Land Cover Database. Retrieved from https://www.mrlc.gov/data?f%5B0%5D=category%3Aland%20cover&f%5B1%5D=region%3Aconus