Natural dynamics and watershed approach incorporation in urban water management: A scoping review.

Several cities are facing water emergencies related to urbanization impact and amplified by climate change. Most of the cities have responded to these crises through short-term measures. However, some cities have incorporated a watershed approach to water management in seeking more sustainable solutions. Although the importance of a watershed approach in land management is generally acknowledged, studies on this topic have typically focused on theoretical models, water management in rural areas or single case-studies of cities or countries. In this research, a scoping review of the literature was performed, based on the PRISMA 2020 statement, in three databases: Web of Science, Google Scholar and SciELO. Forty-one studies were identified analyzing 17 city cases implementing urban actions from a watershed approach in water management. These cities were from the Global North and Asian rising world powers. The lack of results of cities from the Global South, based on the research undertaken, was the main limitation and bias identified. Most of the Global South results identified in this research were theoretical models, scenarios and cases of rural areas instead of urban contexts. The results obtained indicate that the main motivations for cities to implement a watershed approach were water scarcity, floods and contamination of water bodies. The implemented actions focused on the shift from gray to green and blue infrastructure and on conservation measures. Lastly, the challenges to introduce those actions were mainly the lack of economic investment, insufficient experience, stakeholder opposition, and regulatory obstacles. Urban water management could be seen as an opportunity to change the way we relate to urban territory. Incorporating a watershed approach into urban planning and water management could promote more sustainable cities.

The decreasing range between dry- and wet- season precipitation over land and its effect on vegetation primary productivity.

One consequence of climate change is the alteration of global water fluxes, both in amount and seasonality. As a result, the seasonal difference between dry- (p < 100 mm/month) and wet-season (p > 100 mm/month) precipitation (p) has increased over land during recent decades (1980-2005). However, our analysis expanding to a 60-year period (1950-2009) showed the opposite trend. This is, dry-season precipitation increased steadily, while wet-season precipitation remained constant, leading to reduced seasonality at a global scale. The decrease in seasonality was not due to a change in dry-season length, but in precipitation rate; thus, the dry season is on average becoming wetter without changes in length. Regionally, wet- and dry-season precipitations are of opposite sign, causing a decrease in the seasonal variation of the precipitation over 62% of the terrestrial ecosystems. Furthermore, we found a high correlation (r = 0.62) between the change in dry-season precipitation and the trend in modelled net primary productivity (NPP), which is explained based on different ecological mechanisms. This trend is not found with wet-season precipitation (r = 0.04), These results build on the argument that seasonal water availability has changed over the course of the last six decades and that the dry-season precipitation is a key driver of vegetation productivity at the global scale.

Electrical capacitance as a rapid and non-invasive indicator of root length.

Measurement of tree root systems by conventional methods is a Herculean task. The electrical capacitance method offers a rapid and non-destructive alternative, but it has largely been restricted to herbaceous species. The Dalton Model has been the main concept for understanding equivalent root circuitry; it proposed that roots were cylindrical capacitors with epidermis and xylem being the external and internal electrodes. Capacitance (C) therefore varied in proportion to root surface area (A), mass (M), length (L) and relative permittivity of the plant tissue ε(r). We used the capacitance method on forest and plantation trees (13 to circa 100 y.o.) in situ to test hypotheses derived from implicit assumptions about tree-root-soil circuitry. We concluded: C was not confounded by intermingled root systems; C was strongly related to diameter at breast height (DBH); C was less strongly related to DBH for multiple species at the same site; and C was a poor indicator of DBH, M and L across species, ages and sites. We proposed that ε(r) was proportional to root tissue density ρ and fitted a model with P < 0.05 and R(2) = 0.70 when the three immature (13 y.o.) trees were excluded. There was no significant difference (P = 0.28) between the parameters of the tree model (excluding the immature trees) and one of the same form fitted to data from bean (Vicia faba L.; R(2) = 0.55). Together, the data sets suggested (R(2) = 0.94; n = 26) that there may exist a general relationship of this form applied over two orders of magnitude of L.