Figure 1. Distribution of wind speeds (m/s) using (a) a histogram and (b) a box plot for the period 2000–2021.
Figure 1 illustrates the distribution of 10 m wind speeds from three satellite-based reanalysis products using a histogram (Figure 1a) and a box plot (Figure 1b). The histogram shows that wind speeds around 2.5 m/s are the most frequent, with a probability of at least 24%. The box plot (Figure 1b) provides additional statistics on the spread of wind speeds across the three datasets. A comparison indicates that the maximum wind speed in MERRA2 (12.49 m/s) is higher than in CFSR (8.15 m/s) and ERA5 (7.24 m/s). This discrepancy can be attributed to differences in spatial resolution, which is finer for CFSR and ERA5 (20–25 km) and coarser for MERRA2 (50–62.5 km). Overall, the dispersions in CFSR and ERA5 are slightly more similar to each other than to MERRA2.
Figure 2. Wind rose diagram at 10 m altitude over the period 2000–2021 from the CFSR, ERA5, and MERRA2 satellite products.
The wind rose diagram (Figure 2) illustrates the percentage distribution of wind by direction. As noted earlier, the 2–3 m/s wind speed class dominates the overall distribution. For all three satellite products (CFSR, ERA5, and MERRA2), the eastern sector is the most frequent in terms of wind speeds ranging from 1 to 6 m/s. The second most active sector is the southeast for ERA5 and MERRA2, while it is the northeast for CFSR. However, the CFSR product shows the highest wind speed class (7–8 m/s) in the southwest. For this same class, ERA5 indicates occurrences in the east and southeast sectors. In MERRA2, the highest wind speeds are recorded in the west and southwest sectors.
Overall, wind speeds are denser in the east, northeast, and southeast sectors, ranging between 1 and 6 m/s. In addition, the strongest winds (6–12 m/s, exceeding 43 km/h) are observed in the west and southwest sectors.
Figure 3. Monthly distribution of wind speeds (m/s) over the study period (2000–2021) from the ERA5, CFSR, and MERRA2 satellite products.
Based on the monthly variation from 2000 to 2021, Figure 3 shows a heterogeneous year-to-year variability in wind speeds. For the CFSR product, 2001 — particularly in July — experienced the highest wind speeds over the study period, while 2016 recorded relatively lower wind speeds. The diagram also indicates that wind speeds are generally stronger during the warm season (June to September) compared to the cooler season (October to May). For MERRA2, the highest wind speeds were observed in 2019 and 2021, with greater activity during the warm season than the cooler season. For ERA5, the year 2012 recorded the strongest wind speeds over the study area..
Figure 4. (a) Annual variation of precipitation (mm) and (b) frequencies of droughts, light, and heavy rainfall from the ERA5, CFSR, and MERRA2 satellite products over the period 2000–2021.
Figure 4a presents the annual variation of cumulative precipitation over the study period. Peak annual precipitation occurred in 2006 for ERA5 (684.20 mm) and CFSR (362.23 mm), and in 2019 for MERRA2 (619.47 mm). Additionally, the highest daily precipitation was recorded at 116.82 mm (MERRA2, 2019), 115.69 mm (CFSR, 2020), and 72 mm (ERA5, 2018).
Figure 4b shows the frequencies of precipitation classified into three categories: no rain, light rain, and heavy rain. The frequency of no rainfall (P = 0) ranges from 0 to 6% across all three products. Light rain (less than 10 mm) occurs with a frequency between 20 and 52%. Finally, the frequency of heavy rain (greater than 10 mm) is estimated between 42% and 80%, depending on the dataset.
Figure 4 presents the variation of drought and flood events assessed using the 3-month SPI over the period 2000–2021. Table 2 provides the classification of dry and wet events according to SPI values. The MERRA2 product indicates extremely wet years in 2003, 2005, and 2019 (Figure 5a). Similarly, ERA5 and CFSR identify 2019 as a very wet year (Figure 5a). Figure 5b highlights only the extreme events that can lead to human losses and environmental damage. Extremely dry periods were observed in 2000, 2002, 2008, 2009, and 2012 across all three products, while extremely wet periods were recorded in 2000, 2003, 2005, 2006, 2007, 2010, 2018, and 2019 (Figure 5b).
Figure 6. Monthly variation of maximum and minimum temperature (°C) from the ERA5, CFSR, and MERRA2 satellite products over the period 2000–2021.
The interannual variability of maximum and minimum temperatures for the period 2000–2021 is broadly similar across the three satellite products. The CFSR product appears to perform better than the others during the warm season. During this period, maximum temperatures generally peak between 33°C and 44°C, while they decrease during the cooler season from October to May.
Figure 7. Monthly variation of dew point temperature (°C) derived from the ERA5 and MERRA2 satellite products over the period 2000–2021.
To measure the level of humidity in the air, the dew point can be used. The higher the dew point, the greater the amount of moisture in the atmosphere, which directly affects the level of outdoor comfort. The different dew point ranges according to comfort categories are provided in Table 3. During the warm season, dew point temperatures are lower than during the cool season. According to the classification of the Australian Government Bureau of Meteorology, the warm season in MERRA2 corresponds closely to the 15–20 °C class (a combination of heat and humidity). In contrast, during the cool season, atmospheric humidity is higher (Figure 7).
Figure 8. Monthly variation of precipitation and evapotranspiration (mm) from the ERA5, CFSR, and MERRA2 satellite products over the period 2000–2021.
Figure 8 illustrates the interannual variation of evapotranspiration during the study period (2000–2021). Results show that for all three satellite products (CFSR, ERA5, and MERRA2), evapotranspiration increases during the warm season and decreases during the cool season. In addition, Figure 8 highlights that precipitation and evapotranspiration are inversely proportional throughout the months.
Figure 9. Monthly variation of specific humidity (g/kg) and mean temperature (°C) over the period 2000–2021.
Figure 9 presents the interannual variation of specific (or absolute) humidity, expressed in g/kg, derived from the MERRA2 and CFSR satellite products over the period 2000–2021. This parameter represents the number of grams of water vapor in a given volume, relative to the mass of dry air in that volume, expressed in kilograms. Both MERRA2 and CFSR indicate that in April and May, specific humidity reaches its highest values compared to the other months. In contrast, June and July record the lowest levels, while August and September show the second-highest period of specific humidity during 2000–2021. These results are consistent with the monthly variation of dew point temperature.
Figure 10. (a) Increase in sea level (mm) at global and regional scales between 1992 and 2021, and (b) location of the seas.
Figure 10a shows the annual mean variation of sea level rise at three scales: (i) global oceans, (ii) the Arabian Sea, and (iii) the Indian Ocean over the period 1992–2021. The locations of these regions are shown in Figure 10b. During this period, the global mean sea level rose significantly at a rate of 3.013 mm/year. The trend is slightly higher in the Arabian Sea, with 3.397 mm/year, while the Indian Ocean shows a rise of 3.115 mm/year.
Projections of global mean sea level rise for 2081–2100 relative to 1986–2005 are likely to be within the following ranges (given with confidence intervals):
- +0.26 to +0.55 m for RCP2.6,
- +0.32 to +0.63 m for RCP4.5,
- +0.33 to +0.63 m for RCP6.0,
- +0.45 to +0.82 m for RCP8.5.
For RCP8.5, the projected rise by 2100 is between +0.52 and +0.98 m, with an average annual rate of 8–16 mm during 2081–2100.
Source: Image (b) — CoastAdapt: Global climate change and sea level rise.
Abdi-Basid ADAN, 2022
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