Abstract:
Water stored in soils determines how plants grow, how efficiently we irrigate, and how
landscapes respond to drought. These questions are particularly urgent in arid and semi-arid regions,
including much of the Middle East, where freshwater is scarce, soils hold little water, and extreme heat
accelerates evaporative losses. Understanding the physics of soil–water interactions is therefore
essential for designing technologies that improve water-use efficiency and enable sustainable
agriculture. In this seminar, I will examine soil–water interactions through an engineering lens,
presenting two complementary vignettes that connect pore-scale physics to practical solutions for
food–water–climate resilience.
First, I will revisit soil water retention curves (SWRC) – a foundational concept describing
how water is stored in soils as a function of suction. Although SWRC formulations developed over the
past century are widely used, most remain empirical and rely on fitted parameters with limited physical
interpretation. In our recent work, we derive SWRC behavior directly from pore-scale physics by
modeling soils as packings of particles connected by capillary bridges. As water evaporates, these
bridges shrink and the curvature of the liquid interface increases, making further water extraction
progressively more difficult. This simple geometric framework reveals how soil particle size,
wettability, and porosity control field capacity, permanent wilting point, and plant available water.
Second, I will explore when mulching suppresses evaporation—and when it does not. I will
present our bio-inspired superhydrophobic sand mulch, which reduces evaporative water loss from
saturated soils by up to ~80% when applied as a thin surface layer. We will examine how the
effectiveness of mulching evolves as soils dry, and how key factors—including particle size
distribution, water table depth, surface albedo, and thermal conductivity—govern the coupled heat and
mass transport that drives evaporation.
Together, these vignettes will illustrate how combining first-principles soil physics with an
engineering mindset can reveal new strategies for improving irrigation efficiency and strengthening
food–water resilience in water-limited environments.

Bio:
Professor Himanshu Mishra, FRSC, is a scientist-entrepreneur at KAUST dedicated to transforming deserts into permanently fertile landscapes to achieve global food–water–climate security. Over the past decade, his research group has pioneered award-winning soil technologies—most notably CarboSoil™, a #SaudiMade amendment derived from organic waste (e.g., animal manure) that enhances nutrient and water-use efficiency. Unlike conventional soil inputs, CarboSoil offers century-scale impact, unlocking durable carbon credits and catalyzing a circular carbon economy. Mishra’s team has secured over $7M in competitive research funding, published 50+ peer-reviewed papers, and mentored a new generation of innovators. Backed by KAUST, Aramco, King Salman Park, local poultry companies, and nurseries, CarboSoil has advanced to Technology Readiness Level 8, with large-scale deployment now underway across Saudi Arabia. Through his start-up, Terraxy LLC, Mishra is scaling CarboSoil production to support Saudi Arabia’s sustainability giga-projects and global climate goals. His contributions have been recognized by CNN, the World Economic Forum, COP-16 (Riyadh), and the American Chemical Society. Click here for a glimpse.