Ag Proud – Idaho’s Cassidy Woolsey caught up with David Hoekema, a hydrologist with the Idaho Department of Water Resources (IDWR), to discuss this year's unusually dry spring and how it’s affecting the state’s water supply.
The water outlook was optimistic for much of Idaho earlier this year. What were the main drivers behind that optimism?
HOEKEMA: The main driver of our spring optimism in water supply was a near-normal snowpack across much of the state and normal to above-normal reservoir carryover in much of the state (northern Idaho an exception).
What changed so dramatically after April 1 that caused the water forecast to plummet?
HOEKEMA: The most dramatic change since April 1 is a lack of precipitation in April-June with warmer-than-normal temperatures. April through June usually provides about a quarter of our annual precipitation just before summer. This year, we saw only 56% of the median April-June precipitation. Precipitation in April through June helps flush out snowpack in the lower and mid-elevations as temperatures warm through spring, while adding some snowpack at the highest elevations. Temperatures this spring were in the 80th percentile, which is significantly warmer than normal, but not record-setting.
How unusual is it to see this level of dryness and heat in spring and early summer in Idaho, historically speaking?
HOEKEMA: This is the fifth-driest April through June period on record. The five driest April-June periods (period of record 1895-2025) in chronological order are 1919, 1924 (driest 2.11 inches), 1931, 2022 and 2025. In 2025, we received 3.26 inches of precipitation on average statewide.
What are the most immediate concerns for water users and water managers going into August and September?
HOEKEMA: Some smaller reservoir systems will start running out of water at the end of July. Larger systems will likely have to end irrigation season early or reduce diversions to prevent running out of water before the end of the season. However, if a wetter-than-normal summer with higher-than-normal humidity due to monsoonal conditions develops in southeastern Idaho, it could significantly reduce drought impacts in that part of the state. Otherwise, eastern Idaho will likely experience water shortages at the end of the irrigation season. Water users should carefully track their use of storage water and try to stretch it as late into the season as practicable.
Which regions in Idaho are expected to be hit hardest by the current water shortages?
HOEKEMA: Northern Idaho, which is in its third year of drought, will experience water shortages for hydropower production and could experience high stream temperatures due to low baseflows. If the temperature in streams rise high enough, fish kills can result. Yields are expected to be significantly impacted in regions like the Palouse that rely on rain (not irrigation) for crop production. Eastern Idaho is expected to be the most heavily impacted of our irrigated regions, with smaller irrigation delivery systems and water users relying on water rights from tributaries of the Snake River being most severely impacted. Water shortages on the main stem of the Snake River are considered likely during the late-irrigation season or for water users who have limited storage and rely mostly on junior natural flow water rights.
The area with the least impacts is likely to be the southwestern portion of the state for irrigators from Boise, Payette and Owyhee rivers. The snowpack in this region was significantly above normal this winter.
How might this year’s low carryover in some systems affect the 2026 irrigation season?
HOEKEMA: We are expecting low carryover in most reservoirs in eastern Idaho, which means that we will need a larger-than-normal snowpack to have adequate water supply in the coming water year.
Is this year part of a larger trend you’re seeing in climate data for Idaho or the Pacific Northwest?
HOEKEMA: This is a difficult question to answer. We had a number of really dry springs during the 1920s and 1930s; perhaps this cycle will repeat itself. However, with annual average temperatures rising across the state mainly in the winter and summer months, a repeat of dry climate conditions like those seen in the 1920s and 1930s would likely result in greater drought conditions. However, since we cannot predict water supply conditions with any accuracy beyond the current water year, it is hard to predict that we are in a dry cycle like the 1920s and 1930s until we are well into it. Global climate models, which do a poor job of representing precipitation in our region, indicate that as temperatures warm globally, we will see more precipitation; however, that trend is not seen in our current climate record and seems unlikely.
Are there policy or infrastructure improvements that could help mitigate the impacts of future dry years?
HOEKEMA: The Idaho Water Resource Board (IWRB) and private water management entities are taking advantage of excess runoff in pluvial (wetter than normal) years and wintertime baseflows to recharge aquifers. Groundwater pumpers in eastern Idaho have also agreed to reduce pumping, which is leading to a significant reduction in the decline of the Eastern Snake Plain Aquifer. The IWRB, along with many other water management entities across the western United States, are seeding winter storms with silver iodide to try and increase precipitation during winter storm events, which is most effective in normal to pluvial years. Water conservation can also help when conducted in a manner that looks at impacts on the full water cycle. Typically, water conservation is most effective in reducing drought impacts in regions irrigated by groundwater. Water conservation from rivers and streams can have negative long-term impacts by reducing incidental recharge to the underlying aquifers by reducing diversion rates and increasing water consumption by crops.
A general policy of reducing groundwater withdrawals through water conservation, storing more water by injecting it into aquifers in the winter and during spring runoff, and extracting more moisture from storm systems are currently the main approaches being taken in Idaho to mitigate drought impacts.
