# Coupled Spatiotemporal Characterization of Monsoon Cloud Cover and Vegetation Phenology
## 1 Introduction
### Example Study Area  
The location chosen to demonstrate this spatiotemporal analysis methodology is the Dhofar Mountain Chain (Jabal Dhofar) of southern Oman. Jabal Dhofar was chosen on the basis of its monsoon-dominated ecohydrology, endemic biodiversity, and the authors' familiarity with the region. Jabal Dhofar is comprised of three contiguous mountains: Jabal Al Qamar, Jabal Al Qara, and Jabal Samhan. The three mountains each abruptly rise from near sea level to elevations over 1000 m. The eastern Jabal Samhan is the highest, precipitously rising from the coastal plain to nearly 1800 m. Jabal Al Qara lies immediately west of Jabal Samhan. Its coastward face is characterized by deeply incised valleys (wadis), while the rangetop forms a gradual ramp up into the persistently arid desert of the Nejad and the Empty Quarter (Rub' al Khali) of the Arabian Peninsula. The Salalah coastal plain lies between Jabal Al Qara and the Arabian Sea. Jabal Al Qamar is the westernmost of the three mountains, rising more abruptly from the sea and grading more rapidly into the Nejad than Jabal Al Qara. For an introduction to the geography of Jabal Dhofar, see [25]; for broader context on human-environment interactions in the region, see [26; 27; 28]. The climate of Dhofar is dominated by the annual Arabian monsoon. The monsoon occurs as the result of seasonal winds pushing warm, moist air from the Arabian Sea inland onto Jabal Dhofar. This results in persistent ground-level clouds, light rain, and generally cool and moist conditions from roughly mid-June to mid-September. Rain gauges generally record between 100 and 400 mm during the monsoon, accounting for 67.5% of their annual signal [29]. However, gauges incompletely measure the total water delivery because a substantial fraction comes as horizontal precipitation: atmospheric water that is directly captured by collision as suspended droplets are intercepted by objects on the land surface. Horizontal precipitation has been a subject of study for its importance in the local ecohydrology [30; 31; 32; 33; 34] as well as its potential capture for anthropogenic uses (e.g., [35; 36]). While some horizontal precipitation occurs on the coastal plain, the majority is located on the coastward slopes of Jabal Al Qamar and Jabal Al Qara. The relative geographic isolation and distinct microclimate of Jabal Dhofar contribute to high endemic biodiversity and a unique floral assemblage, as documented in detail by [37; 38]. The coastward slopes and wadis of Jabal Al Qara and Jabal Al Qamar are each home to a seasonal cloud forest ecosystem that is dominated by the endemic _Anogesisus dhofarica_ tree, while broad rolling grasslands dominate the ridges and plateaus. A diverse fauna includes the iconic and critically endangered Arabian Leopard [39]. Camels, cattle, goats, and feral donkeys feed on the woodlands and grasslands and are found throughout. Figure 1, panels A-D show the way in which the topographic, atmospheric, and biospheric factors that are described above contribute to multispectral reflectance as observed by MODIS. Topographic relief (data: Shuttle Radar Topography Mission (SRTM), Figure 1A) limits the extent to which monsoon cloud cover and precipitation, blown northward from the Arabian Sea during the monsoon, can penetrate inland. The landscape is dry before the monsoon (Figure 1B), but water is provided through monsoon precipitation (Figure 1C), which results in extensive vegetation greening during and immediately following the monsoon (Figure 1D). Example VNIR field spectra (E and F) demonstrate the differences between green vegetation, non-photosynthetic (e.g., senesced) vegetation, soil, and cloud at \(<\) 3 nm spectral resolution. MODIS is a multispectral sensor, integrating the true VNIR  
reflectance continuum (solid lines) into four measurements (points) as characterized by the sensor spectral response function (dashed lines), resulting in differences in NDVI (inset text labels).