Author Contributions
Conceptualization, A.B. and M.E.M.; methodology, A.B.; software, A.B. and D.S.; validation, A.B., D.S., M.E.M., R.C., R.B., and S.M.; formal analysis, A.B.; investigation A.B., and D.S.; resources, A.B., and M.E.M.; data curation, A.B., and D.S.; writing—original draft preparation, A.B., and M.E.M.; writing—review and editing, A.B., M.E.M., R.C., R.B.S., S.M., and D.S.; visualization, A.B.; supervision, M.E.M., R.C., R.B.S., S.M.; project administration, A.B.; funding acquisition, R.C. All authors have read and agreed to the published version of the manuscript.
Acknowledgments
We gratefully acknowledge the anonymous reviewers and editor of the paper in providing critical and constructive comments, which has helped us to significantly improve the manuscript. We are also grateful to the India Meteorological Department, NOAA, NCDC, UCSB and Climate Hazard Groups for providing long-term observatory data. We also appreciate the assistance of Ehsan Sharifi (Institute of Meteorology and Climatology, University of Natural Resources and Life Sciences, Vienna, Austria), Kishore Pangaluru (Department of Earth System Sciences, University of California, Irvine, CA 92697, USA) for their valuable suggestions regarding the methodology section of this paper.
Figure 1.
Location of the Bhilangana river basin in Uttarakhand, India. The IMD meteorological observatories and major settlements in the study region are indicated by blue and red solid triangles respectively. The background image is ASTER GDEMV2, derived from USGS.
Figure 1.
Location of the Bhilangana river basin in Uttarakhand, India. The IMD meteorological observatories and major settlements in the study region are indicated by blue and red solid triangles respectively. The background image is ASTER GDEMV2, derived from USGS.
Figure 2.
Spatial distribution of mean annual and seasonal rainfall (mm). Top panel distribution is from reanalysis and bottom panel from satellite-based gridded datasets derived using GEE.
Figure 2.
Spatial distribution of mean annual and seasonal rainfall (mm). Top panel distribution is from reanalysis and bottom panel from satellite-based gridded datasets derived using GEE.
Figure 3.
Mean distribution and variance of station-based and gridded rainfall products. Annual, seasonal (a,c), monthly (b,d) rainfall and variance, respectively for the period from 1983 to 2008.
Figure 3.
Mean distribution and variance of station-based and gridded rainfall products. Annual, seasonal (a,c), monthly (b,d) rainfall and variance, respectively for the period from 1983 to 2008.
Figure 4.
(a–c) are showing the relationship between the gridded and observed datasets (r2), (d) Bias, (e) RMSE and (f) CDF for all datasets with the corresponding station for the period from 1983 to 2008.
Figure 4.
(a–c) are showing the relationship between the gridded and observed datasets (r2), (d) Bias, (e) RMSE and (f) CDF for all datasets with the corresponding station for the period from 1983 to 2008.
Figure 5.
Spatial distribution of trends in annual and seasonal rainfall along with their statistical significance (1983–2008) (Top panel showing CHIRPS reanalysis and bottom PERSIANN-CDR satellite-based data products respectively).
Figure 5.
Spatial distribution of trends in annual and seasonal rainfall along with their statistical significance (1983–2008) (Top panel showing CHIRPS reanalysis and bottom PERSIANN-CDR satellite-based data products respectively).
Figure 6.
Spatial distribution of magnitude of trend in annual and seasonal rainfall, (Top panel showing a spatial tendency of CHIRPS and bottom panel PERSIANN-CDR data respectively).
Figure 6.
Spatial distribution of magnitude of trend in annual and seasonal rainfall, (Top panel showing a spatial tendency of CHIRPS and bottom panel PERSIANN-CDR data respectively).
Figure 7.
Long-term temporal distribution of monthly rainfall and annual magnitude of trends in mm/decade (a) monthly values from 1983 to 2018, (b) mean annual and seasonal rainfall for three distinct rainfall phases with error bars from 1983 to 2018 (c) box and whisker plots show monthly rainfall values from 2009 to 2018 (d,e) mean annual, seasonal and monthly rainfall of station observed data for two different time periods (1983–1997; 1998–2008).
Figure 7.
Long-term temporal distribution of monthly rainfall and annual magnitude of trends in mm/decade (a) monthly values from 1983 to 2018, (b) mean annual and seasonal rainfall for three distinct rainfall phases with error bars from 1983 to 2018 (c) box and whisker plots show monthly rainfall values from 2009 to 2018 (d,e) mean annual, seasonal and monthly rainfall of station observed data for two different time periods (1983–1997; 1998–2008).
Figure 8.
(a) Spatial distribution, (b) statistical significance level and (c) trends in annual and seasonal rainfall from 2009 to 2018 respectively. Top panel showing annual and seasonal rainfall distribution from 2009 to 2018, Middle panel indicate the level of significance (at 95% confidence level based on MK test), Bottom panel showing annual and seasonal trends of rainfall for the same period, where blue and red color indicates increasing and decreasing trends, respectively.
Figure 8.
(a) Spatial distribution, (b) statistical significance level and (c) trends in annual and seasonal rainfall from 2009 to 2018 respectively. Top panel showing annual and seasonal rainfall distribution from 2009 to 2018, Middle panel indicate the level of significance (at 95% confidence level based on MK test), Bottom panel showing annual and seasonal trends of rainfall for the same period, where blue and red color indicates increasing and decreasing trends, respectively.
Figure 9.
Taylor diagram compares observed and gridded datasets (Notations, “Jan to Dec” are used for defining months, “Ann to Win” for annual and seasons, “obs” for the observation stations and “C” and “P” denote CHIRPS and PERSIANN-CDR respectively).
Figure 9.
Taylor diagram compares observed and gridded datasets (Notations, “Jan to Dec” are used for defining months, “Ann to Win” for annual and seasons, “obs” for the observation stations and “C” and “P” denote CHIRPS and PERSIANN-CDR respectively).
Figure 10.
(
a–
d) Regional consequences of alternations in annual, seasonal and monthly rainfall pattern from 1983 to 2018. (
a,
b) show some effects of decreased rainfall; (
c,
d) the state of property after a major rainfall event. Localities of photos a-d are shown in
Figure 1. Photos: A.B.
Figure 10.
(
a–
d) Regional consequences of alternations in annual, seasonal and monthly rainfall pattern from 1983 to 2018. (
a,
b) show some effects of decreased rainfall; (
c,
d) the state of property after a major rainfall event. Localities of photos a-d are shown in
Figure 1. Photos: A.B.
Table 1.
Data used to estimate long-term rainfall variability in the Bhilangana river basin.
Table 1.
Data used to estimate long-term rainfall variability in the Bhilangana river basin.
Station Observed Data (Collected from IMD) |
---|
Station | Location | Period | Elevation (m) | Available Observations (%) |
---|
Lat. | Long. |
---|
Mukhem | 30.34 | 78.28 | 1983–2008 | 1981 | 95.8 |
Tehri | 30.22 | 78.26 | 1983–2008 | 676 | 91.3 |
Narendra Nagar | 30.09 | 78.17 | 1983–2008 | 1037 | 81.3 |
Gridded Data (Downloaded through Google Earth Engine Platform) |
Data product | Year | Source | Grid Spacing |
CHIRPS | 1983–2018 | UCSB/CHG | 0.05 arc degree |
PERSIANN-CDR | 1983–2008 | NOAA/NCDC | 0.25 arc degree |
Table 2.
Mean annual, seasonal, and monthly distribution of station and gridded datasets in the Bhilangana river basin for the period from 1983 to 2008.
Table 2.
Mean annual, seasonal, and monthly distribution of station and gridded datasets in the Bhilangana river basin for the period from 1983 to 2008.
Data | JAN | FEB | MAR | APR | MAY | JUN | JUL | AUG | SEPT | OCT | NOV | DEC |
Station | 63.7 | 78.3 | 66.8 | 50.6 | 71.3 | 112.3 | 227.9 | 223.8 | 144.5 | 40.0 | 10.3 | 30.3 |
CHIRPS | 36.8 | 27.1 | 35.4 | 17.4 | 46.1 | 90.0 | 290.6 | 263.8 | 141.0 | 23.6 | 5.4 | 20.8 |
PERSIANN-CDR | 55.7 | 54.9 | 40.4 | 31.7 | 36.1 | 140.5 | 347.1 | 410.5 | 201.5 | 42.4 | 13.4 | 28.1 |
Data | Annual | Pre-monsoon | Monsoon | Post-monsoon | Winter |
Station | 1313.4 | 154.3 | 1014.8 | 48.3 | 96.0 |
CHIRPS | 1119.7 | 188.7 | 708.6 | 50.3 | 172.3 |
PERSIANN-CDR | 998.0 | 98.9 | 785.4 | 29.1 | 87.7 |
Table 3.
Statistical indices to check the spatial similarity between observed and gridded datasets (CHIRPS and PERSIANN-CDR) for the period from 1983 to 2008.
Table 3.
Statistical indices to check the spatial similarity between observed and gridded datasets (CHIRPS and PERSIANN-CDR) for the period from 1983 to 2008.
Statistical Indices with Units | CHIRPS | PERSIANN-CDR |
---|
Tehri | N.Nagar | Mukhim | Tehri | N.Nagar | Mukhim |
---|
RMSE (mm) | 29.60 | 24.66 | 21.58 | 81.24 | 96.20 | 111.30 |
MAE (mm) | 30.20 | 26.31 | 66.54 | 49.76 | 83.09 | 66.54 |
Bias (mm) | 4.59 | 6.26 | 9.88 | 16.88 | −23.4 | −29.5 |
MBias (mm) | 0.93 | 0.99 | 1.62 | 0.77 | 2.11 | 1.61 |
RBias (%) | 0.06 | 0.08 | 0.41 | 0.29 | 0.35 | 0.39 |
CC | 0.85 | 0.67 | 0.69 | 0.74 | 0.60 | 0.75 |
Table 4.
Annual and seasonal rainfall distributions and trends (1983–2008) in the Bhilangana river basin for ground station records.
Table 4.
Annual and seasonal rainfall distributions and trends (1983–2008) in the Bhilangana river basin for ground station records.
Station | Sen.’s Slope (mm/decade) |
---|
| Annual | Monsoon | Post-Monsoon | Winter | Pre-Monsoon |
---|
Mukhim | Distribution | 1473.7 | 1095.8 | 56.7 | 169.9 | 151.2 |
Trend | −2.04 | −3.79 | −0.88 | −0.01 | −0.68 |
Tehri | Distribution | 710.8 | 469.9 | 22.2 | 125.6 | 92.9 |
Trend | −12.26 | −7.46 | 0.00 | −0.71 | −0.31 |
Narendra Nagar | Distribution | 1400.4 | 1249.9 | 29.5 | 65.5 | 55.5 |
Trend | −32.82 | −22.37 | −0.82 | −2.56 | −0.95 |
Table 5.
Monthly rainfall distributions and trends in the Bhilangana river basin (mm/decade, 1983–2008) based on station observed data.
Table 5.
Monthly rainfall distributions and trends in the Bhilangana river basin (mm/decade, 1983–2008) based on station observed data.
Station | | JAN | FEB | MAR | APR | MAY | JUN | JUL | AUG | SEPT | OCT | NOV | DEC |
---|
Mukhim | Distribution | 56.2 | 81.5 | 53.8 | 42.8 | 54.6 | 163.4 | 342.9 | 357.9 | 231.7 | 45.0 | 11.7 | 32.3 |
Trend | −0.34 | 0.71 | 0.20 | 0.42 | 0.42 | −0.31 | −0.70 | 0.62 | 0.10 | −0.60 | 0.00 | 0.00 |
Tehri | Distribution | 42.5 | 56.0 | 32.0 | 32.0 | 29.0 | 66.0 | 159.8 | 170.4 | 73.7 | 20.5 | 1.7 | 27.1 |
Trend | −0.13 | −0.00 | −0.00 | −0.00 | −0.11 | 0.10 | −0.80 | −0.10 | −0.11 | −0.10 | 0.00 | 0.00 |
Narendra Nagar | Distribution | 43.7 | 29.2 | 23.3 | 26.5 | 28.0 | 145.7 | 382.7 | 493.7 | 296.2 | 30.5 | 33.1 | 39.6 |
Trend | −0.62 | −0.42 | −0.70 | 0.00 | −0.30 | −0.91 | −8.43 | −12.40 | −2.92 | −0.51 | 0.00 | 0.00 |
Table 6.
Annual and seasonal trends in frequency of rainy days in the Bhilangana river basin (days/decade, 1983–2008).
Table 6.
Annual and seasonal trends in frequency of rainy days in the Bhilangana river basin (days/decade, 1983–2008).
Station | Annual | Monsoon | Post-Monsoon | Winter | Pre-Monsoon |
---|
Mukhim | −6 | −8 | −2 | −1 | 0.00 |
Tehri | −7 | −3 | 0.00 | 0.00 | 0.00 |
Narendra Nagar | −9 | −11 | 0.00 | 0 | 0.00 |
Table 7.
Annual and seasonal rainfall trends in the Bhilangana river basin (mm/decade, 1983–2008).
Table 7.
Annual and seasonal rainfall trends in the Bhilangana river basin (mm/decade, 1983–2008).
Data | Annual | Monsoon | Post-Monsoon | Winter | Pre-Monsoon |
---|
CHIRPS | −14.82 | −24.14 | −9.60 | −12.60 | −3.12 |
PERSIANN-CRD | −6.91 | −5.12 | −0.71 | −2.91 | −1.32 |
Table 8.
Monthly rainfall trend of gridded datasets (mm/decade, 1983–2008).
Table 8.
Monthly rainfall trend of gridded datasets (mm/decade, 1983–2008).
DATA | JAN | FEB | MAR | APR | MAY | JUN | JUL | AUG | SEPT | OCT | NOV | DEC |
---|
CHIRPS | −1.08 | −0.51 | −1.13 | 0.12 | −1.60 | −3.10 | −9.42 | −9.44 | −5.71 | −0.81 | −0.30 | −0.42 |
PERSIANN-CDR | −1.11 | −0.12 | −0.50 | −0.60 | 1.21 | 1.42 | −2.31 | −3.50 | −0.60 | 1.12 | −0.11 | −1.41 |
Table 9.
Monthly distribution, trends, and uncertainty (mm/ decade, 1983 to 2018).
Table 9.
Monthly distribution, trends, and uncertainty (mm/ decade, 1983 to 2018).
Distribution | JAN | FEB | MAR | APR | MAY | JUN | JUL | AUG | SEPT | OCT | NOV | DEC |
---|
1983–2008 (CHIRPS) | 36.82 | 27.11 | 35.44 | 17.44 | 46.11 | 89.90 | 290.60 | 263.83 | 141.11 | 23.61 | 5.60 | 20.84 |
1983–2008 (Station) | 47.4 | 55.6 | 36.4 | 33.8 | 37.2 | 125.0 | 295.1 | 340.6 | 200.6 | 32.0 | 15.5 | 33.0 |
2009–2018 (CHIRPS) | 40.6 | 55.5 | 58.91 | 35.62 | 67.52 | 161.62 | 460.92 | 434.82 | 207.92 | 36.33 | 3.91 | 2.42 |
Relative Uncertainty | 11.4 | 15.9 | 3.9 | 3.6 | 3.2 | 6.5 | 0.3 | 0.1 | 3.0 | 15.9 | 18.2 | 16.3 |
Sen’s slope using CHIRPS (2009–2018) | 0.79 | −2.1 | 2.91 | 1.61 | 3.69 | 7.54 | 6.09 | −2.02 | −8.21 | −1.88 | −0.06 | −1.18 |