Examining Changes to the Temporal Distribution of Seasonal-to-Annual Precipitation across the Mid-Atlantic Region,

Transcription

1 Examining Changes to the Temporal Distribution of Seasonal-to-Annual Precipitation across the Mid-Atlantic Region, Michael Marston PhD Student, Virginia Tech

2 Precipitation (mm) Precipitation (mm) Motivation Precipitation for Blacksburg, VA Fall 1982 Fall Count Mean 8.0 mm 6.2 mm Std. Dev. 7.3 mm 10.9 mm Total Precip mm mm * Only days with precipitation were used to calculate mean and standard deviation 30-year average Fall precipitation for Blacksburg ~ 222 mm Precipitation Amount per Day (September November 1982) Precipitation Amount per Day (September November 2013)

3 Background Research suggests precipitation characteristics will change as the global climate warms (IPCC 2013). Atmosphere s moisture holding capacity increases ~7% per 1 C (Trenberth et al. 2003). Changes in precipitation patterns and distributions have been elusive to document (Schleiss and Smith 2016). Continued warming stresses the need to understand past changes in precipitation patterns for water-sensitive stakeholders. Research Questions Did precipitation distribution characteristics change from 1982 to 2016 across the Mid-Atlantic Region? Did streamflow variability coincide with changes in the distribution of precipitation from 1982 to 2016?

4 Gini Index Developed in the early 1900s by Corrado Gini. Used primarily in economic studies (wealth distribution). Several studies have examined regional global scale changes in precipitation using Gini Index. Rajah et al. (2014) determined the Gini Index is sensitive to the number of wet days, proposed a wet-day Gini Index.

5 Wet-Day Gini Index 1. Eliminate days with zero precipitation Precipitation Data 9.7 mm 0.5 mm 1.3 mm 1.8 mm 13.0 mm 6.6 mm 0.8 mm 5.1 mm 3.8 mm 7.6 mm Sorted Precipitation Proportion of Total Precipitation Cumulative Proportion of Precipitation Sum = 50.2

6 Wet-Day Gini Index y-axis x-axis Cumulative Proportion of Precipitation Number of days with precipitation n =10 1/n = 0.1 Cumulative Proportion of Days with Precipitation A Area B = 0.28 Area A = 0.5 Area B = 0.22 B GI = 2 * Area A = 0.44

7 Precipitation (mm) Precipitation (mm) Blacksburg, VA 50 Precipitation Amount per Day (September November 1982) GI = Precipitation Amount per Day (September November 2013) GI = 0.70

8 Study Area & Data Ten States (276,000 km 2 ) Global Historical Climatology Network (GHCN) Daily National Centers for Environmental Information (NCEI) ~ 100 Stations met 90% data completeness constraint

9 Methods Wet-day Gini Index For this study: winter DJF, spring MAM, summer JJA, fall SON, annual water year A Gini Index was calculated for each spring, summer, fall, winter and annual time increment from 1982 to 2016 for all stations meeting data completeness constraint (90%). Time series of Gini values for each seasonal and annual time periods were subjected to a Mann-Kendall Trend Test to determine changes over the historical record.

10 Annual Results 88 Stations # stations % stations Negative Trend (SS) Negative Trend No Trend Positive Trend Positive Trend (SS) Positive trend: Precipitation became more unevenly distributed from Negative trend: Precipitation became more evenly distributed from

11 Winter Season Results 95 Stations # stations % stations Negative Trend (SS) Negative Trend No Trend Positive Trend Positive Trend (SS) Positive trend: Precipitation became more unevenly distributed from Negative trend: Precipitation became more evenly distributed from

12 Spring Season Results 102 Stations # stations % stations Negative Trend (SS) Negative Trend No Trend Positive Trend Positive Trend (SS) Positive trend: Precipitation became more unevenly distributed from Negative trend: Precipitation became more evenly distributed from

13 Summer Season Results 91 Stations # stations % stations Negative Trend (SS) Negative Trend No Trend Positive Trend Positive Trend (SS) Positive trend: Precipitation became more unevenly distributed from Negative trend: Precipitation became more evenly distributed from

14 Fall Season Results 98 Stations # stations % stations Negative Trend (SS) Negative Trend No Trend Positive Trend Positive Trend (SS) Positive trend: Precipitation became more unevenly distributed from Negative trend: Precipitation became more evenly distributed from

15 Fall Season Results Sen s Slope = T-Value = 1.96 P-value = 0.02 Sen s Slope = T-Value = 4.06 P-value = < 0.01

16 Fall Season Results GI = 0.43 GI = 0.73

17 Streamflow GHCN Station Total SON Precip. Vs. Total SON Streamflow ( ) SON GI Vs. σ SON Streamflow ( ) 7409 r = 0.39 (p-value=0.02) r = 0.57 (p-value<0.01) 1480 r = 0.80 (p-value<0.01) r = 0.31 (p-value=0.06)

18 Conclusions The temporal distribution of precipitation changed for many stations across the Mid-Atlantic region from 1982 to Larger number of stations experienced trends toward a more uneven distribution of precipitation. Changes were most pronounced in the annual, winter, and fall time series of Gini Index values. Noticeable spatial patterns of trends. Preliminary results indicate potential relationships between the temporal distribution of precipitation and intraseasonal streamflow variability. Future Work Examine precipitation characteristics using additional methods. Further examine relationships between changes in the temporal distribution of precipitation and streamflow variability.

19 Examining Changes to the Temporal Distribution of Seasonal-to-Annual Precipitation across the Mid-Atlantic Region, Michael Marston PhD Student, Virginia Tech

20 TMIN TAVG

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26 RESULTS GI trends of fall season precipitation from

27 CLIMATOLOGY a. b. Average number of precipitation events (a) and average precipitation(b), per fall season from 1981 to 2015

28 CLIMATOLOGY a. b. Trend (a) and significance of trend (b) in average fall precipitation from

29 CLIMATOLOGY a. b. Trend (a) and significance of trend (b) in average number of fall precipitation days from