Guest post by: Sebastian Busby, Erika Brown, Logan Craig, Krissy Lindsay undergraduates in Environmental Science, University of Idaho
Turf-grass lawns are everywhere here in the U.S; from the “front lawn” outside every suburban housing development to the broad spanning fields found in public parks. Lawns happen to be an essential part of our Euro-American cultural identity – which is why we quite vigorously put them in places they don’t necessarily belong. Out here in the West, the climate is characteristically warm or hot and dry during the summer, and either cold or mild and wet during the winter. Annual precipitation occurs primarily during October through May, which creates the yearly dilemma of everyone’s lawn turning a nice crispy golden brown during the summer in the absence of irrigation. The majority of water in the West comes from snowpack melt transported long distances from the major mountain basins (Sierras, Rockies, Cascades), or from limited regional aquifers. With water resources continually being taxed by a growing number of multiple and complicated needs, can we conserve some of our resources by easing our need to have a well-watered lawn?.
As part of our undergraduate senior-thesis we examined the sustainability of lawns at the University of Idaho (UI) in Moscow under current and projected future climates from the prospective of water demand, and developed an acceptable alternative. We used a historic monthly average of precipitation and temperature for Moscow using historic climatology from 1981-2010 and a simple water balance equation without lateral surface exchanges from Dingman (2002) and code provided here. This water balance model accounts for snowmelt contributions and estimates potential evapotranspiration using a simple temperature index approach. We found that there is about 240mm of unmet water demand (difference between potential evapotranspiration and available water) each summer. Thus, a well-watered green lawn requires irrigation to make up the difference during the summer months.
With the help of the Applied Climate Science Lab at UI, we obtained monthly climate projections for Moscow from the latest set of global climate modeling experiments being used in the next IPCC report. Using 28 different models and two different emissions pathways we considered both the average change in monthly temperature and precipitation from the models and a “worst-case” scenario that considers the second warmest and second driest model.
We illustrate projected change in temperature and precipitation averaged across all models for the more aggressive emission pathway (RCP8.5) for three different decades in the future. Warmer temperatures and overall drier summers seem to be the theme.
With these estimates of future precipitation and temperature, we determined how much annual water-loss was expected from the soil (evapotranspiration) – and therefore how much additional watering would be required to keep lawns alive. While projections vary, between 50 and 200 additional mm of irrigation demand could occur by mid-century and up to 350 additional mm of irrigation by 2100.
The University pumped 33.8 million gallons from the regional aquifer to water lawns during the summer of 2011; based on this figure, using the 8.5 W/m2 average scenario, UI would have to use 45 million gallons by 2050 and 59.2 million gallons by 2100 – respectively 33% and 75% increases. The regional Grande Ronde aquifer which is the primary water for Moscow and Pullman has seen a decline by approximately 1 ft/year since the 1930s and additional irrigation in a changing climate will tax already impacted water resources.
To determine the viability of an alternative, native climate-adapted landscaping planted recently (1-5 years ago) was sampled to establish survival rates. Despite poor soil quality (old railroad-beds), the total survival rate was surprisingly high: 87%. Finally, to determine whether patrons of the UI would support further implementation of adapted landscaping, we conducted a survey from the undergraduate population. The results showed that student’s did have an attachment to lawns, but greatly underestimated the amount of water required to keep them alive, and after being informed, overwhelmingly supported further planting of adapted landscaping.