Is “Average” Changing in Your Area in North Dakota? North Dakota Precipitation Trends Are Changing

By Lucy Sledge

Ranchers’ operations can be drastically affected by weather conditions and there is nothing we can do to change the weather. We can only change how we react and prepare for what conditions are thrown at us.

One great risk management tool is Pasture Rangeland, Forage (PRF) Insurance which provides loss payments when the area has a below average precipitation. When this insurance tool’s triggering factor is pegged to an average, it is vital to know if precipitation trends are changing in your area.

Are conditions getting drier in the central part of the country? Is there a higher likelihood of below-average rainfall or snowfall for certain months? When deciding on Pasture, Rangeland, and Forage (PRF) insurance it is important to know if there is a higher frequency of below-average precipitation and for which months.

I looked at precipitation trends in Missouri, North Dakota, and South Dakota over 30-year and 10-year timescales, from 1994 and 2014, respectively. I used USDA PRF grid cell data for four grid cells from each region of the state (Northwest, Southwest, Northeast, and Southeast) and counted the number of above-average years versus below-average years. I did this for each of the 11 monthly ranges USDA provided and averaged the grid cells for the region to give us a general sense of trends.

For simplicity, I then turned the “counts” of below versus above average into percentages to directly compare 10-year and 30-year frequency. You will notice that in the 10-year trends, there are non-even percentages; for example, 75% of July-August periods which would suggest 7.5 out of the last 10 years, and the uneven number is attributed to the averaging of multiple grid cells. Because PRF triggers not by the percentage by which we are below average just that we see less than 100% of average precipitation, I will talk about above or below average precipitation years in terms of frequency, not quantity at which they are above or below average.

However, for context, I’ve selected a “representative” official National Weather Service reporting site for annual precipitation totals. In highlighting annual precipitation trends we can gain further insight into if years have been getting overall drier – i.e. those PRF below-average periods may be more drastic. In the graphs below, precipitation for each year over the last 30 years is displayed as a dotted line, and the solid line illustrates the trend.

Please note that the average precipitation is on rolling averages and may not directly line up with PRF Insurance precipitation triggers. These averages are also based on large regions of a state and do not correlate to any one specific grid. These averages should be used for context and not to decide coverages. Talk to a PRM Risk Management Advisor for interval selection recommendations.

NORTHWEST NORTH DAKOTA

Over the last 30 years, we have seen a decrease in annual rainfall in northwest North Dakota. The graph below shows a general trend (solid line) towards less annual precipitation over the last 30 years.

Looking at the monthly periods with PRF data, the highest likelihood of seeing below-average precipitation is from January through June. The majority of years since 2014 have had below-average precipitation during these months. Over the last 30 years, more than 60% of January through Mays had below-average precipitation too. There is not only short-term but long-term support in below-average conditions in the winter and spring. In summer, there are no major trends for above/below average precipitation. The months with a higher likelihood of wetter than average conditions are October through December, supported in both 10-year and 30-year trends. The bottom line is that our most likely below-average months are January through April with an increasing likelihood that May through June is also drier than average, too.

NORTHEAST NORTH DAKOTA

Unfortunately in northeast North Dakota, there is no reliable climate site with precipitation data for the last 30 years. To give us the “bigger picture” for this region I took the average percent of normal for multiple PRF grid cells since 1994. We see a decreasing trend of percent of normal precipitation over the last three decades – below-average precipitation is more common now.

A closer look at PRF grid data illustrates that every single period has had more below-average years than above over the last decade. Every single year since 2014 has been below average for the February – March period with eight of ten years below average from November to February. Comparing the 30-year averages to the 10-year averages there is a higher likelihood of drier-than-average conditions from April through August and again from September to October, occurring more than 50% of the time. Though our highest likelihood of seeing below-average precipitation is from November to April there is an increasing frequency of below-average precipitation during much of the year now too.

SOUTHEAST NORTH DAKOTA

Using Jamestown, ND as a reference point for annual precipitation we have seen a decrease in annual precipitation for the city over the last 30 years, a loss of roughly 4”. Annually, we are getting drier.

Monthly precipitation averages show that the months most likely to experience below-average conditions are January to March. These likelihoods are reflected in both 10-year and 30-year averages. The most likely periods to see wetter-than-average conditions are from May – June, August – September, and November – December. Not only are they most likely periods to be above-average the frequency of above-averge years is increasing: 70% frequency since 2014 as opposed to 50% since 1994. Our most frequent below-average times of the year are winter with an increasing frequency of below-average precipitation in June – July. 

SOUTHWEST NORTH DAKOTA

In southwest North Dakota, we have seen a decrease in annual precipitation – it is getting drier, on average 6” less precipitation annually over the last 30 years.

When we break this down into monthly periods for PRF purposes, the most likely months to see below-average rainfall are November through April with the majority of years in the last 10 seeing below-average conditions. Below-average conditions have been observed in nearly every January – March period since 2014. The only period that has seen more frequent above-average conditions is July – August. The bottom line is that drier-than-average conditions are most likely from October through May with the summer months seeing equal chances of above/below normal rainfall.

Conclusion

North Dakota sees most frequent below-average precipitation in the late Fall and Winter months with some bleed-over into early Spring. Unlike Missouri though, over the last 30 years, we have seen less annual precipitation across North Dakota. In southern North Dakota, we see below-average conditions from October to April with the highest likelihood of above-average precipitation in July and August. This is reflected in both our 10-year and 30-year trends. On the north side of the state, we also see our highest frequency of below-average precipitation from January through April. There is an increasing likelihood of below-average rainfall in the summer months in northern North Dakota with even some indications of drier conditions year-round.

So is it getting drier? For the Dakotas, annual precipitation has been trending downward over the last 30 years and the frequency of below-average periods is increasing. In Missouri, the answer isn’t that simple – while yearly precipitation may have increased slightly over three decades, monthly examination indicates an increasing frequency of below-average periods.

In many cases, the periods that displayed a higher frequency of below-average years since 1994 continue to display this in the last 10 years, and at a higher frequency too. The months that already tended to be below average continue to do so in the last decade. Furthermore, though we have seen some small increases in the frequency of wetter-than-average conditions, for many regions the number of wet periods versus dry has not drastically increased in the last 10 years.

_{Disclaimer: This report is not a recommendation or advice for crop insurance coverage. Talk to a licensed Risk Management Advisor for any policy recommendations. Precision Risk Management is an equal opportunity provider. Go to PrecisionRiskManagement.com/legal for all disclosures.}