Jennifer Volk, Extension Environmental Quality and Management Specialist; jennvolk@udel.edu and Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
Did you know that 2015 was the warmest year on record for our planet since the record began in 1880! Looking locally, the annual average temperature in Delaware has been on the rise too, increasing 0.2°F per decade. So, our annual average temperature today is about 2°F warmer than it was a century ago.
Delaware’s Division of Energy and Climate led the development of a Climate Change Impact Assessment to investigate what kind of changes in temperature and precipitation we may experience in the future and how those changes could impact the resources in our state. In this assessment, climate data observed in Delaware was used to downscale global climate models to determine the range of potential future conditions we could see here. What will ultimately happen in the future depends on a number of factors. One of those factors is the rate at which humans emit carbon into the atmosphere — so the assessment looks at potential futures under both high and low carbon emission scenarios.
Like our recent trends, the projections show annual average temperatures continuing to increase out through 2100. Seasonally, spring and summer temperature increases are expected to be greater than the increases anticipated in fall and winter. For Delaware summers at the end of the century, temperature is projected to increase by as little as 3.5°F under low carbon emission scenarios to as much as 15°F under high carbon emission scenarios. Extremely hot days are expected to occur more frequently in the future too. Our local historical record shows that we had fewer than 5 days/year on average when temperatures exceed 95°F; but, by 2100, this frequency could increase 4-10 fold. The probability of heat waves is also expected to increase. And, the worst is when it’s not only hot, but also dry. The prediction is that the number of hot, dry days will increase from about 20 days/year in our historical record to 60-90 days/year by 2100. It won’t just be warmer during the day either. Nighttime temperatures are not expected to drop as much as they have in the past, with more nights staying warm (>80°F).
All of these temperature changes have obvious implications for crop production. Yield reduction is predicted for many crops, particularly C3 plants (soybeans, most vegetables). In general, high temperatures negatively affect the plant reproductive cycle. In corn for example, periods of excessive and/or prolonged heat, especially when it is also dry, can decrease pollen viability, impact the timing and length of pollen shed and silking, and result in the silks drying out. Even if fertilization is successful, heat stress in the weeks following could cause the ovules to abort. Similarly in vegetables, higher temperatures and warmer nighttime temperatures could result in reduced fruit and seed development. Heat build-up in plants could also result in reduced quality with conditions like scorched stems and leaves, sunburned fruits, or blossom end rot. Hotter summers will increase the incidence of split sets in bean crops and require shifts in processing vegetable production scheduling.
To cope with these temperature increases, researchers are always exploring new varieties that are more heat and drought tolerant. We also know that irrigation is a tool that helps mitigate hot, dry conditions in crops and it is already widely employed in our state. Also, healthy soils tend to retain more moisture, so employing soil health practices is a good strategy too.
It will be interesting to see how hot we get this summer and where the annual average temperature for 2016 ultimately falls in the record books. If you are interested in learning more, visit the Delaware Climate Projections Portal where you can chart and download projection data for 14 weather stations across our state: http://climate.udel.edu/declimateprojections/