Climate change causes major disruptions globally and is beginning to show measurable changes locally that affect many aspects of life, including cultivation.
Whether working in agriculture or a backyard garden, most successful harvests are based on good weather forecasting predictions, which are based in large part on historical record.
What happens when March rains dwindle or April showers fall short? Historically, spring is known as the stormy season, but a review of local weather patterns in Pittsburgh over the past five years show March and April to be among the drier months of the year.
Yet, Pittsburgh weather isn’t drying up; instead, we are experiencing more rain during the summer and fall compared to a traditionally wet spring.
According to US Climate data between 1981 to 2000, the Pittsburgh region averaged 34.8 inches of precipitation per year, for an average of 2.9 inches each month. Weather data over the past five years indicate an average precipitation of 43.9 inches, or around 3.7 inches per month.
This surge in stormwater was predicted by EPA climate change models, and unfortunately, it doesn’t always come in gentle showers that are beneficial for plants. Instead, much of the precipitation comes in droves during heavy rain events that can cause severe flooding.
These strong storms are known to strip topsoil from the land, putting heavy pressure on waterways. All of this puts Southwest Pennsylvania in line with some two thirds of the world’s land area that will “experience wetter, more variable conditions as the Earth warms, making extreme rainfall and flooding more likely,” as reported by Forbes.
See these trends in the following tables, with average precipitation by month:
Average Precipitation in InchesMonth1981-20102000-20132018-2022Changejan2.9-2.5-0.4feb2.2-3.8+1.6mar3.0-3.2-0.2apr3.03.13.2-0.2may3.34.13.7+0.4jun3.04.04.1+1.1jul3.44.34.2+0.8aug3.03.64.2+1.2sep3.03.44.7+1.7oct2.22.94.1+1.9nov3.2-2.6-0.6dec2.7-3.4+0.7Total34.8-43.9+9.1Average2.9-3.7+0.8Table 1. Precipitation by Month, with the planting season highlighted in green
As the table indicates, March and April saw slight reductions in average rainfall between the 1981-2010 period compared to the last five years, but this decrease was swamped by the much larger increases of precipitation during other months, such as nearly a two inch increase during October.
In total, we are seeing over nine additional inches of precipitation each year than we were over the previous three decades, a 26% increase. That’s about 3/4 inch per month. To illustrate greater detail on the rate of this increase, the period growing season from April to October (highlighted in green) during 2000-2013 shows how fast this trend is expanding.
If you water your lawn or garden, or you irrigate row crops, this can have a meaningful impact on your water demand. We estimate that plants need one inch of water per week plus ½ inch for every 10 degrees above 60°F. We’ve compiled a simple calculator using the average record high temperature for each month to show how much irrigation plants might want each month.
High TempsAprilMayJuneJulyAugustSeptemberTemp (f)808790919088Precip (in)3.23.74.14.24.24.7irrigation2.12.01.71.71.61.0Table 2. Irrigation requirements beyond rainfall assuming maximum temperatures by month
To use the data, simply multiply your growing area (converted to square inches) by the irrigation totals for each month. This gives the volume in cubic inches. Convert that number to gallons by multiplying by 0.004329 and this offers a rough estimate of how many gallons you might need each month for irrigation. Divide that number by 4.3 for an approximate volume each week.
As our climate changes, so will many common agriculture practices. Some plants will fare better than others. Precipitation is one factor among others, such as temperature, invasive species, and commodity prices, which put pressure on crops we need to sustain our economy and food supply. How much precipitation we get during each event is just as important. As we look ahead and plan the upcoming growing season, be sure to adjust your work accordingly.
