Table 4.
MK and Sen's slope results for the annual time series (rainfall, maximum temperature, minimum temperature, average temperature, and PET).
| Stations | S | VAR(S) | Z | Sen's Slope | p-value | Signific. | tau |
|---|---|---|---|---|---|---|---|
| Rainfall | |||||||
| Anger | 2.000 | 2842.000 | 0.019 | 0.105 | 0.985 | 0.005 | |
| Gida | −31.000 | 2058.330 | −0.661 | −4.181 | 0.509 | −0.095 | |
| Nekemte | 50.000 | 2842.000 | 0.919 | 5.754 | 0.358 | 0.123 | |
| Shambu | −106.000 | 2842.000 | −1.970 | −10.220 | 0.049 | * | −0.261 |
| Ehud Gebeya | −2.000 | 950.000 | −0.032 | −0.026 | 0.974 | −0.011 | |
| Jarnet | −21.000 | 1433.670 | −0.528 | −3.927 | 0.597 | −0.083 | |
| Haro | −37.000 | 817.000 | −1.260 | −8.429 | 0.208 | −0.216 | |
| Kiramu | −7.000 | 697.000 | −0.227 | −5.600 | 0.820 | −0.046 | |
| Maximum temperature | |||||||
| Anger | 68.000 | 950.000 | −2.174 | −0.080 | 0.030 | * | −0.358 |
| Gida | 113.000 | 1257.660 | 3.158 | 0.062 | 0.002 | ** | 0.489 |
| Nekemte | 177.000 | 3141.660 | 3.140 | 0.030 | 0.002 | ** | 0.407 |
| Shambu | 159.000 | 2058.330 | 3.483 | 0.060 | 0.0004 | ** | 0.489 |
| Minimum temperature | |||||||
| Anger | −26.000 | 950.000 | −0.811 | −0.021 | 0.417 | −0.137 | |
| Gida | 114.000 | 1096.660 | 3.412 | 0.065 | 0.0006 | 0.543 | |
| Nekemte | 206.000 | 2842.000 | 3.845 | 0.035 | 0.0001 | ** | 0.507 |
| Shambu | 134.000 | 1833.330 | 3.106 | 0.070 | 0.002 | ** | 0.447 |
| Average temperature | |||||||
| Anger | 56.000 | 950.000 | −1.784 | −0.040 | 0.074 | −0.295 | |
| Gida | 110.000 | 1096.660 | 3.292 | 0.064 | 0.0009 | ** | 0.524 |
| Nekemte | 232.000 | 2842.000 | 4.333 | 0.041 | 0.00001 | *** | 0.571 |
| Shambu | 176.000 | 1833.330 | 4.087 | 0.083 | 0.00004 | *** | 0.587 |
| PET | |||||||
| Anger | −56.000 | 950.000 | −1.784 | −5.454 | 0.074 | −0.295 | |
| Gida | 16.000 | 1096.67 | 0.453 | 0.646 | 0.651 | 0.076 | |
| Nekemte | 85.000 | 3141.670 | 1.499 | 1.038 | 0.134 | 0.195 | |
| Shambu | −20.000 | 1833.330 | −0.444 | −2.068 | 0.657 | −0.067 | |
*, ** and *, **, and *** represent variables of significance (* <0.05, ** <0.01, *** <0.001). A positive (+) value represents an increasing (upward) trend and a negative (−) represents a decreasing (downward) trend over time. The trends in the annual mean at six stations (Shambu, Gida, Ehud Gebeya, Jarnet, Kiramu, and Haro) revealed that precipitation is decreasing. Except for Shambu station, annual precipitation shows a non-significantly decreasing trend. On the other side, Anger and Nekemte stations show a non-significant (p > 0.05) increasing trend. The annual average temperature of three stations (Nekemte, Gida, and Shambu) indicates statistically significant increasing trends (p < 0.05), while the Anger station shows a non-significant (p > 0.05) increasing trend. The time series potential evapotranspiration was estimated for four stations (i.e., Arger, Gida, Nekemte, and Shambu). Only these stations have time-series temperature data to calculate potential evapotranspiration. There was no statistically significant increasing or decreasing trend in the average annual potential evapotranspiration for all stations (Anger, Gida, Nekemte, and Shambu) during the study period.